The aircraft only have HE rounds in the game and a 20mm round would penetrate the armor up to 2 inches thick the MRAPs and Ifrits should be disabled with ease and the BRT and APCs shouldn't be able to withstand more then a 40 rounds barrage of 20mm gun. I actually have witnessed (in my army career) 20mm impacting on soft targets (personnel) it rips the personnel apart and the projectiles from the rounds that impact the ground within a 5 meter radius of the personnel are incapacitated and targets up to 10 meters are severally injured. As for the vehicles, the rounds hit the target and devastate the target. You have to realize its not just a few 20mm rounds impacting on a target but anywhere from 10-100 round burst depending the pilot/co-pilots time holding down the trigger. The rounds are impacting the vehicles from the top down usually which is the weakest part of the armor besides the belly, so there is no reason you should not be able to kill a foot soldiers and immobilize the armor on a strafing run.