PA's MIBs and their employment has been sort of an enigma but what I've gathered so far is;
First of all we must not confuse being mechanised with being armoured. Being solely mechanised doesn't mean that it is armoured. That's why British army has divided it's mounted infantry in to armoured (equipped with Warrior IFV) and mechanised (equipped with bulldog APC, similar to M113).
Now what I think is that we've been confusing mechanised inf with armd inf.
Armoured inf has "vehicle centric approach" while mech has "soldier centric approach".
Vehicle centric approach means that being IFV equipped the vehicle will provide the main base of fire, while the infantry which has dismounted just near or even at the objective will form the assault element. Thus vehicle gives them the fire team which clears the enemy threats, suppresses enemy so the infantry can advance and also protect the vehicle. This also allows for quick remounting and continuation of advance.
Soldier centric approach means that DISMOUNTED inf will provide both the fire team and assault team. The dismounted inf will itself form the base of fire as well as the manoeuvre element. The APCs after dropping the inf at a forming up place or short of objective outside enemy's range will fall back and remain on call after the objective has been achieved for remounting (In PA's case ATGM protection may be provided by the M113s).
Thus the difference between a PA SIB and MIB is that while SIB relies on S&T for motorised transport and hence is more or less static without it, MIB has its own organic tracked transport.
So, the role of MIB in PA is not to fight as armoured inf i.e leading charges themselves, but to provide inf over all terrains while keep up with the tanks.
