AI Mortars, HMG and IG units frequently are taken well foward within, say an infantry battalions footprint and thus get too much forward into the combat lines, when instead they should be placed further back (like normal Arty) in covered (rear slope) terrain, for better security.
That could be dealt with properly by a human player (micro managing, preserving under Regt control)), but the AI will frequently put them in hazards.
I figured it´s doesn´t really matter if a suport unit is either "line support", or just "support". It´s currently taken well forward, when attached to a battalion. I Think these s/b excluded from the normal formation code and other, better rules applied instead.
For my own Estabs I solved that partly, by using more varied unit mixes and attaching/detaching support units to fit a particular battle type. That involves units that have heavy support weapons integrated within coys, or have them entirely stripped from these and kept under divisional command. That´s just an expedient though and does not keep the AI from assigning them back forward into the frontlines and thus in unnecessary hazards again.