I have no idea why my troops defend that bad there.
They are in a city (high autoentrench) and you can attack only from one direction,
so no concentric bonus.
All the tanks and SMG are no problem for the fins, but the staff officers are

Is it the additional punch of the mortars ?
The problem here is probably that that infantry type is a rear area type
and i was not able to shoot at [:(]. Looking at the last game and this attack i think
the mortars could be overpowered considering their costs and their rear area status.
Beeing in defense you can´t defend against that weapon.