IMHO something wich would be realistic is to put a sort of "don't moove your stik too fast" command when you get hit by a AP or HE shell...like a noise after the impact wich would get the tank out of combat for some seconds.
I'm artillery officier and I lead a batterz of M109KW long range tanks,I won't list the munition we have, but for example firing a normal Iron shell (artillery shell) caliber 155mm with a impact fuse (detonator) and not retarded won't enter in a M1 or Leopard2 armor (80-90K lb tanks), but be sure the impact will shock/kill who's inside.
The same is for a 75mm caliber, with maximal charge we talk about 250 to 400 m/s. If you want I can calculate the nr of joule you get on the impact wich, with or without AP, would at least shock who's inside for some seconds/minutes.
I saw a Gren-tank 2000 fire some short bursth with his 36mm cannon against a tank target (a old T68 tank of 100K lb). The armor was still perfectly intact, but with the impact the tank moved some meters...you can just imagine how would be inside the tank.