I've been thinking. What makes concussive firepower so powerfull is basicly the increased range. In the range 7,8 and 9 hexes, concusive rule tripple the effective firepower of tanks versus infanteri in buildings. At other ranges its only an increase of 50%.
Combined fire: in some cases I find combined fire natural and work as it should. These cases are
1) 2-4 infanteri attacking a single tank at point blank range.
2) 2 or 3 shermans attacking a single tiger at short range.
Regarding entrenchments in buildings: I like it a lot and it makes a lot of sence. This could also be usefull in a lot of other scenarios I guess, and maybe especially for future stalinggrad scenarios. If you in addition allow the russians to setup an AT gun in a fortified building ...