I'm pretty sure that anything will penetrate the rear armor 100% of the time. Just sayin, that's a pretty glaring weakness.
Plus, soviet mines should be everywhere.
Panther?
SU-85 is the only non doctrinal unit that can penetrate panther rear 100% of the time.
T34 can bounce even from that and at panther vet2 T34 will have ~60% to penetrate panther rear.