There is no way to make pillboxes in the system. They would already be on map and were more plentiful than wooden machinegun nests (which is what bunkers describes). I'd install both pillboxes and bunkers as immobile vehicles with facing. Differing in their weapons and thickness. Based along the border, military posts, and highway checkpoints. As well as immobile SAM batteries. Anti-tank ditches on military posts would also add flavor.
Reducing day delta to 1 hour and keeping movement the way it is would mesh well I think. Also, reducing map scale back to 1km per hex would be neat. To bad you can't edit sight ranges. Longer attack ranges across the board would have a realistic effect.
I think whether the engineer is a split unit rather than a combined unit effects its basic engineer value. In your game the inability to recombine seems to have a greatly negative effect. What is the 6x fatigue modifier you mention (as the reason for using KG setting)?