You miss my point.
1) we don't have that modeled, and it would be a major change, including major additions and adjustments to the damage model itself, as well as chaning what makes an HE shell go boom.
2) we really can't do it perfectly (or even very) realistically, because our armor isn't actual steel, and our tanks aren't actually there.
3) HE rounds didn't always cause spalling, or kill the crew, or didn't always do anything. Having them always damage tanks in AH would be monsterously unfair, and essentially turn it into WoT, where a 37mm weapon could eventually kill a King Tiger given enough time and HE rounds. If we don't make it 100% of the time, then we introduce an random number generator that decides if your crew will be killed by spalling or not.
4) It would result a HUGE degredation of skill amongst GV'ers. There would be no encouragment to use tactics and ambush more powerful vehicles, or use the M18 to sprint in around the flanks, when you can just spam HE at enemies you lack the skill to deal with.
5) All perks for all tanks would have to be completely redone. The Tiger II would need a FAR smaller perk price if HE rounds can take it out from the front. The Panther would likely be dropped to the high single digits, and the firefly would go back to 4-5 perks.
So come up with a system that adresses all those issues, and then submit it to AH. If not, then don't bother; it wouldn't work well even assuming people don't get lazy, and it would destroy the GV aspect of the game when they do.