That's interesting. I have tried different versions of this FF, finding it unbalanced to let the reinforcements enter in round 3. Playing both sides solitare, the Germans were wiped out in round one as they were longing for reinforcements in round 3. So then I tried bringing the re-inf. into round 2 and the play was great!
The firefight was so close and ended 14-15 to the Soviets. The pioneers attacked on the left but met too much resistance, to be able to reach the demoliotion hexes. This gave the Soviets 9 point and while the Germans made them pay in blood, the Soviets just managed to hold off, as the Germans attacked one last time a hit unit, and got 2 less than what was needed. So, in the end a very close and extremely engaging firefight where German reinforcements came into round 2, not round 1. Higly recommendable.