[Imp]

Firstly 0.4 would be blindingly quick for that time cause you can call in fire anywhere virtualy instantly.
So using the z fire sighting rounds & plotting fire for effect would be in my opinion far more realistic.

As I said test in the editor then make a custom OOB with adjusted mortars, not sure if it can still be embeded might have to do the mortar as an individual section.

For a campaign anyway if you keep them alive they will soon become better, if they start at 1.2 wont be long before they are doing 0.4