There are no range buffs with vet for the pit that I know about...
Actually against good players you struggle to vet the pit up. It gets xp for kills not damage so people who don't leave their units lying around in the open to be mortared don't lose so many models to it. Helps the infantry vet up as they are up against lower health models.
Ostheer has plenty of tools for taking pits out, frankly keeping one alive for more than a few minutes is a challenge.
Talking of vet though other than vet3 with a health buff and smoke ( I think) at vet2 the vet is useless. There is a recharge time buff for bombard, which is bugged and unused.
true it doenst get any range increase it seems, oddly i could have bet.
but i digged some numbers out for the xp needed:
mortar pit:
-480
-960
-1920
Leig:
-840
-1680
-3360
seems like its really easy to vet up
but maybe my stats site is not correct since it only shows up 3 vet levels for the LEIG, which one is accurate? i used http://www.stat.coh2.hu/vetraw.php?filename=brit_3_inch_mortar_team_mp