I'm not a follower of "1=1 per hex, 20 hexes deep" doctrine, I always thought it's waste of forts which build soo slow, and allowing to be destroyed piecemeal. Of course it's important not to get encircled, but a 3-hexes deep defensive line (3 divs, 1 div, 1 brigade) line was ok in 1942 - I was pushed back of course, but it was because of overall lack of strength of Soviet divisions and lack of ability to concentrate more troops per hex. In 1943 it's a line of 1 corp + 2 divs or 2 corps + 1 div, one empty hex and 1 div or brigade in second (actually third) line. I have to make this empty space, because otherwise units rout and this costs a lot of troops, more than combat. Now my stack is just pushed back. Strong stacks force Germans to use deliberate attacks by 6 to 9 panzer/inf divisions and this costs them a lot of movement points plus they have to mix forces from 2 or more corps, losing CV in the process. That way they cannot utilize their greatest strength - high number of fast good quality units that can deeply penetrate due to lower MP penalty. It's just that finding balance between depth and strength at front that is hard to do, you cannot go full depth or full front.