On the balance of ground fire:

mortars can keep ground attack with direct fire range so they can do defensive fire, but not actual arty, they cant push an HMG directly. maybe slightly lower than direct fire range too account for scatter, but when taking fir they die really quick so….. shrug

pack howies like pack howie and leig can have ground attack be equal too direct fire range too help justify their higher cost vs mortars. but im afraid theyd just use ground attack right infront of a HMG too have scatter kill it, but then it would be so close it would risk dying too infantry push.

autocannons, can just lose ground attack. but id like if they could get an ability like the crusader AA in vanilla with short range too shoot down walls n trees n stuff, and maybe too deal extra dmg vs inf but idk if it would or should be any more effective than the actual atuocannon itself.

Autocannons currently with the attack ground ability is currently the most OP thing for early tier allies and axis. The .222 and m15 are the prime examples of these things. The m15 is the most OP autocannon because it has the farthest range and is the most durable of early autocannon vehicles for the allies. It can eviscerate axis MGs and expensive axis squads. Loosing the attack ground would help immensely with the balance of autocannon vehicles.  I personally don’t think ground attack with mortars is as overpowered, however when there are is more than one mortar I can see the issue.

on another note, heres what id do

: remove ground attack from autocannon vehicles

: remove ground attack and idle fire from mortars, you pay muni, you get indireect fire barrage.

:mortar emplacements can ground attack and idle fire within direct fire range, and can pay muni too fire beyond, maybe with longer range / more fire rate / cheaper price too make up for its stationarity

:LEIG and pack howitzer can fire HE shells directly, with low shell travel time- think of sherman 75 HE round or panzer 4 F1 HE shell, with same direct fire range as those vehicles. this helps justify their more expensive price over the mortar, and gives the docs that have em (US AB, UK Lowland, OKW Luft, OST Volks) a usually needed lil option that can help be used aggressively, or defensively. Historically, the IG-18 was definitely made for direct fire in mind, although the pack howitzer was more artillery focused it could (and probably would in use with the US AB and UK AB) be used as a direct fire gun in a pinch.