Yeah, I was right. As described in MgT's Central Supply Catalog, PGMPs/FGMPs only require operators to be wearing battle dress because the weapons are (uniformly) bulky. In LBB4 (Mercenary), the PGMP-13 and FGMP-14 require operators to be wearing battle dress because the powered armor serves as the weapons' recoil carriage!
(PGMP-14 and FGMP-15 have gravitic recoil compensation and do not require battle dress.)
I like the visuals of the older versions better. It's not just a big blaster to wave around -- it turns your trooper into a walking direct-fire artillery piece!