- The Idea that the Mortar Pit should be replaced with a regular one.
The only problem with this light arty pieces is how easily it can use ambient buildings to its advantage and there fore avoid all incoming fire. And the survivability bounus it attains once vet.
In order to fix that, we can increase the free space requirement around the emplacement while its being built. For example it should require a minimum of 6-9 meters of free area for construction, ie you can't just build it right near an ambient building. This way, recon and pak 40 can still threaten it.
TLDR1. Building The Mortar Pit should require a wider distance from ambient buildings, 2. Reduce the survivabilty bonus at higher levels of vet.
Mortar pits were actually even more unique prior to release than they are now. You could toggle them to fire longer ranged shells at cost of accuracy and damage, or heavy shells for opposite. They became implausible BS when it was removed and basically got both without the need for micro.
I don't think hiding behind ambient building make it any more OP or easy to use than any artillery unit in the game which can do the same thing, and it's larger size means it's actually more susceptible to being hit. Of course their immobility and durability makes up for it.
Here's a simple solution: nerf range but keep long distance barrage range? I believe other artillery units have that now.
Another idea that could be applied to emplacements in general: remove the Forward Assembly/ garrison requirement buff and put it in as a veterancy bonus. You still get the bonuses but you need to do more than simply build emplacement near a Forward Assembly. Mortar Pit being able to fire faster just because it's close to a building, as opposed to garrisoning a unit inside, mitigated the risk of tucking a unit into a pit behind a building. If anything emplacements became too specialized that only one made sense at the front (bofors), one behind buildings (mortars) and one behind bofors (17 pdr.).
A more novel idea is that mortar pits only use one mortar until certain conditions are met, like Forward Assembly built or unit is garrisoned, so that if you want to BS camp with mortar pit behind a building you have to spend even more time and resources for it. Other factions already live with this restriction, as Ostheer you only fire two mortars shells at a target, if you got two mortar units trained and sent out. Even now mortar pits still have an advantage due to being emplacement, plus they would need to build something they'd always build close to the pit in the first place. TLDR it's a straight up nerf that is removed after you build things next to it, not before.
A fourth idea: nerf emplacements's durability but restore it when close to Forward Assembly, and remove the FA buffs to emplacements and put them elsewhere, ie as vet1 unlocks.
The idea is that the Forward Assembly becomes the weakpoint to emplacements' durability, so if an opponent wants to somewhat neutralize or make easier to destroy an emplacement, they attempt the alternate target that is the Forward Assembly; destroy the FA your emplacements are in trouble. Opponents have no such options against emplacements, it's just slug it out until it's dead while you repair, or slug it out and hope the attacks also kill the engineers.
A simpler alternative to the fourth idea: emplacements REQUIRE a Forward Assembly to be build. So if you want to build that pit behind a building then you need to make sure that Forward Assembly's aura can reach it, and then first build Forward Assembly. Not as easy as it sounds though, you might have to buff FA's durability or reduce cost and build time for sake of balance: emplacements would be useless if it's always going to take too long to get to emplacements. Maybe also make Infantry Sections also build Forward Assembly?