The armor of the T-34 is 45mm all around.
It's only 40mm on the back, which is technically thin enough to be penetrated by a PTRS/PTRD landing a perfectly flat shot, at close range, with tungsten ammo. Pretty unlikely. Top and bottom are thinner, of course.
BTW all german tanks except the panther and tiger are penetratable on the side by soviet AT rifles.
The Panzer 4 and other medium tanks with 30mm armor can be penetrated, so long as the angle isn't very much off perpendicular. The 14.5mm round apparently had a reputation for shattering on impact, which made the drop-off in penetration due to the angle off of perpendicular even sharper. While the PTRS/PTRD is perfectly capable of penetrating 30mm armor at close range, battlefield conditions make it much less capable.
Of course, that's arguing real-life rather than the tweaks they had to do to performance to get combined-arms warfare (sort of) working at this scale. Strangely the tweaks have made the ATR perform
significantly better against the T34 than it should, while their increase in performance against the Panzer is much smaller. Doesn't help that the Germans have all the tungsten ammo, and it gives such a massive boost in the game.
I'm really surprised know why the germans get a soviet AT rifle and not their own 7,92 mm PzB.39 but cosidering it had even poorer penetration this would ruin balance.
It's particularly amusing with all the arguments about how enemy loadouts are unrealistic. Here we've got an enemy weapon used with such frequency that it has its own inventory designation.