In the downing of Flight 752 we’ll look at three kilogram verses fifteen kilogram warheads and a direct hit versus a ‘proximity’ detonation. , 
A proximity detonation is preferred over a direct hit in surface to air missile defense against hostile aircraft. 
The rationale behind designing anti-aircraft, surface to air missiles, for proximity detonations is simple. The initial rationale for proximity was a narrow miss in the early days. As accuracy and dependability improved, proximity fuses were often kept, in addition to impact fuse, as it had been discovered an aircraft’s air-frame can actually contain the effect of the explosive warhead, depending on the design of the aircraft and the location of impact. A modern missile guided to proximity detonation (a mere few feet away from the aircraft) is likely to inflict greater damage, more often than not, because the shrapnel from the high explosive warhead has a better chance at penetrating and damaging a wider area of the target, more readily compromising critical flight control systems (especially wing-flaps and associated hydraulics.) This is why light mobile combat systems such as the Russian Strela 10’s early and middle models (through 1988) with a three kilo warhead had both impact and proximity fuses. The Strela, proximity fused three kilogram warhead used by Iraq in Desert Storm (1991) was capable of taking down the American A-10 ‘Warthog’ (two A-10s shot down by this missile, according to the American military), one of the toughest planes to shoot down with ground-fire in modern combat (to this day.) 
By the era of the Stinger, very effective against Soviet helicopters in Afghanistan, missiles had become so maneuverable and accurate, the Stinger was only adapted for a proximity fuse in later (recent) development phases; to be effective against very small (difficult to direct hit) UAVs (drones.) The three kilo (average) warhead launched with a MANPAD (shoulder launched) surface to air missile, it was likely a Stinger FIM-92J (proximity fused warhead), provided by CIA to the so-called ‘moderate opposition’, is what had brought down a SU-25 in Syria:
As well, it may have been (likely was) a Russian made IGLA (SA-24) with a 2.5 kilo warhead brought down an AN-30 over Ukraine:
What is noticeable with the much larger AN-30 is, with the starboard (right) engine on fire after having been hit with a 2.5 kilogram MANPAD warhead, the plane is stable and keeps course as the crew is bailing out. What the crew understands is, the heat of the fire will quickly compromise the aluminum alloy of the plane’s wing structure, which should soon buckle and there will be no control. It is better to parachute out before that happens.
What we have (very briefly) looked at to now is what 3 kilo heat-seeking warheads can do to military planes, the smaller planes tend to go down more quickly, more often than not, with immediate loss of control, is the main difference. The smaller SU-25 jet’s wing mounted engines (the heat-seeking target) are more tightly integrated to the main air-frame and wing control flaps. A larger plane has a better chance at keeping control, but the control won’t last long if the plane is on fire, and fire is what happens when heat-seeking warheads hit jet engines.
Of course, bailing out with parachutes is not an option for the passengers and crew of a Boeing 737-800, a medium size passenger jet not all that much larger than the AN-30 in the (2nd, above) video.
All of the preceding would be consistent with Iran initially reporting they believed a ‘technical issue’ or engine fire was the culprit that brought down Flight 752 if they were unaware of a missile launch.
Now, the Flight 752 story begins to become problematic at many levels.
A MANPAD heat-seeking missile has small cross-section and radar signature but it does show up on radar. With its’ small signature, it might be understandable if a MANPAD were missed or somehow interpreted as an anomaly by civilian operators of traffic control at an international airport, but that shouldn’t be the case with a larger missile. For example, a Stinger MANPAD has a missile diameter of 70mm versus 235mm diameter of the Tor m1 missile attributed to shooting down Flight 752. One should expect a Tor M1 missile(s) would have been picked up by the civilian air traffic control radar at Tehran’s international airport. So, already the Iranian story is showing a hole, when it is supposedly ascertained no one but the military knew what had happened. Over at John Helmer’s blog the (increasingly demonstrated to be false) Iranian story is set out very well. 
““The plane has been hit at a low altitude by a short-range missile with a small warhead and proximity fuze,” Hajizadeh reported. “It has exploded at the proximity [of the aircraft]; so the plane has found the chance to fly for a while; it hasn’t exploded in the air. After hitting the ground, it has collapsed. So no one at the [Iran Civil] Aviation Organisation knew about it, and I should defend my dear brothers there.””
This is not a particularly convincing deceit on more than one ground; on top of no explanation as to why the civil airport radar didn’t pick the missile up, there is a problem with the missile strike description. We have seen what a 3 kilogram warhead can do to aircraft already. The Tor M1 warhead is fifteen kilograms, this is NOT a small warhead (the Iranians are claiming a 7 kilo warhead but I don’t buy it and 7 kilos is still double what had brought down the AN 30.) A ‘proximity’ strike (mere feet from the aircraft with the thoroughly modern Tor system), should be devastating to a Boeing 737. By comparison, the superman of SAM systems, the S-400, uses a 24 kilo warhead in typical air defense configuration (excludes the ‘below the horizon, search and destroy’ warhead, an entirely different purposed missile.)
Then, John Helmer weighs in as this reporter is composing:
Russian military experts doubt details of missile shoot-down of Ukrainian Flt 752, missile track and timing, aircraft damage. Vzglyad reports assessment that Iranian faction politics decided on limited hang-out, lesser of two evils. https://t.co/EXot9s92ILpic.twitter.com/Latkh92hh7
— Dances_with_Bears (@bears_with) January 14, 2020
In the initial reporting from the Iranian side, we’d seen 
“Qassem Biniaz, an official at the Iranian Ministry of Roads and Urban Development, told state news agency IRNA that an engine caught fire and the pilot was unable to regain control” 
Firstly, loss of control is not the immediate effect of an engine fire, loss of control comes after the aluminum alloy structure has been compromised, this is when there will be no regaining of control, but this may actually what had been referred to.
The Western reaction:
“…the U.S. manufacturer does not believe a 3-year-old airplane that just underwent inspection days before caught on fire.
“That aside, an engine fire doesn’t rule out a missile,” the source said. “A missile strike itself could’ve caused the fire. The explanation is ridiculous and the conclusion is more than suspicious.” 
The Boeing ‘source’ is actually helpful, if he only knew how: a plane with an engine fire from a missile, that keeps a bit of control, is going to, nearly every time, come down from having been hit by a MANPAD.
We do know the pilot had been able to turn the plane back towards the airport, and the preceding would be consistent with both, a MANPAD strike and a lack of complete understanding of the circumstance; before the Iranians had time to line up all the possible duck configurations, discover the facts and make a decision as to how to proceed with what this author is convinced had been a MANPAD take-down of Flight 752 by a Western intelligence cell inside Iran.
It follows, ultimately Iran decided to take on a false accountability for two simple but compelling reasons; 1) the international institutions and Western press are bought little different to referees and judges can be bribed to determine a boxing match outcome & 2) Western cells operating within Iran to point of bringing down Flight 752 would be a serious black eye to the domestic perception of Iranian security, weakening the regime in the public perception. Falsely swallowing responsibility is the path of least immediate damage to the Iranian governing institution, both internally and externally.
The stupidity on the Western side in this is, yeah, you hit the ayatollahs below the belt and got away with it, but you also likely convinced them there can never be a genuine détente with Western institutions, ever.
Is something like this what happened? Lots of ‘smoke to clear’ yet in emerging picture but the entire business just goes on smelling wrong –
“It is sometimes very hard to tell the difference between history and the smell of skunk” -Cicily Isabel Fairfield
3 Author’s training at the USA Air Defense Artillery School, Ft Bliss
5 Flight 752 discussion begins about 1/2 way into Helmer’s article: http://johnhelmer.net/the-fog-of-war-gorilla-radio-discusses-the-russian-focus/