Why do the medium tanks have so small target size?This will make them harder to hit by AT guns.
I believe that's the intention. Their small target size contribute to their survivability. This is just complaining that the british tank can actually last more than 10 second in combat, unlike the t34 76 and even 75mm sherman. The jackson have size 24 and the jpz4 have size 17, and it's one of the biggest factor in the difference between their survivability.
Raise the price of the cromwell or nerf the gun if necessary, but the cromwell's small size allow it to actually fight the german and not die horribly.
stuff like the halftrack and 222 should be a bit smaller.