In the real world SAM's are not very lethal, unless they are compared to AA guns. IIRC, Dupuy did an analysis in his "The Arab-Israeli wars" and determined that it took over 1,000 SAM's to bring down a Jabo. I don't think he counted mission kills.
A small correction. The Larger SAM's do have directional warheads. Think of them as flying shotguns. The cone is fairly wide, 30 degrees or so. Some of the ManPADS have shaped charge warheads. They need it since the exhaust of a jet is much more violent the the explosion of a small warhead.
The inside of a jet combustion chamber is hotter and subject to more force then what can be produced by a couple of kilos of explosives.
The usual result of an up the tail pipe hit by a ManPADS is a flameout. If the jet is high enough it is possible to restart a hot engine. If you are flying a helio, you have a serious problem.
I think Dupuy is a little off, since he just looked at Egypt vs the IAF. Here is a link to the raw data for Vietnam;
http://www.afa.org/magazine/Sept2004/0904vietnam.pdf
Sucess rates vary from a high of 5.7% in '65 to 0.9% in '68.
NVA just used Large SAM's. IIRC, the Redeye was about the only ManPADS around at that time. I don't think the strella showed up intil the early 70's. I could be wrong, I'm not an equipment guy.
It takes millions of shells to bring down a Jabo on the average. Or at least that was the numbers from WW2. Not much real world useage of AAA since then. Upper limit on most SPAA systems is about 12,000 feet, so by the time you figure in slant range, the engagement cone is extremly small. Plus the Jabo has an advantage of having what ever it shoots eventually hitting the ground. Gravity ALWAYS wins. Doesn't matter what the contest is.
Modern targeting systems are good enough to get 20mm shells into a 4 hex by 4 hex area from waaay above the max range of any SPAA. So straffing runs against the AAA from beyond the range of the AAA is not only possible, but normal.
SP will not and can not model modern air power. A B-2 dropping JDAM's from 70,000 feet is untouchable by anything made by human hands. The JDAM has a CEP of 10 meters. It leaves a hole larger then that, so having an opponent wipe out a 7 hex area anytime he wants to won't be much of a game. Remember a B-2 can do this 48 times before it has to go home for more bombs. Very few people want to play a game where their part of the game consists of watching their stuff blow up. You will find out what the Taliban found out. You can't hide, you can't run, you can't fight back. All you can do is quit or die.
What I would like to see is some sort of break off test. Something along the lines of what an infantry unit takes before close assaulting a tank. Where if the Jabo starts a pass and the flak an Sam's are to heavy, the attack run is aborted. The Jabo doesn't RTB unless it is hit, but the pass isn't carried out either. That way air strikes would be something more then free points for your opponent, without dominating the game.