HMGs vs APC role?

[Weeble]

What round will the AI choose to fire against an opponent with both armoured and unarmoured areas, given both HE & AP/SLAP loadout, if it chooses to fire at all?

I was trying to recreate the 42 Cdo RM assault on Limbang, Sarawak, 12/62. I had reduced the armour on landing barges to recreate the improvised armour craft used. These had 1.5" wood + sand-filled backpack sides, and the front loading ramp welded up (?).

I gave them 1 side & rear steel armour, 2 front [Hull]. 1 rear turret, 0 front & sides (glass bridge & wheelhouse). 0 top armour.

In I vain tried to get my TKNU rebels to fire at the oncoming 'Z' craft before they reached the Police wharf. I tried altering ammo loadouts & weapons for the TKNU rebels MG and had to settle for .50cal instead of the (actual) .303 Bren. Eventually I assumed it was a SNAFU on my part and gave up.

However...

I have since tried to get the AI to react fire onto bulldozers backing towards (and through!) LMG, MMG and HMG squads, but unless I go up to a weapon where the HE round has a pen value I get no joy. I know the bulldozer has an extra tough HEAT front hull dozer blade for its 2 steel front hull armour, but all other facings are zero.

Do weapons without a HE penetration value not AI fire at targets with only some armoured faces (such as the US M48A1 Chaparral, which has a soft turret sides and rear)?

Am I expecting too much from the AI, as most human players would jump at the chance of firing at the "soft spot" on an otherwise armoured vehicle?