This is a good question @scrapiron, I would imagine that the RF measurements and diagraming do take into account the mounting plate. Without working at it a bit, an MR would be challenging to mount on a ceiling or a wall without the mounting plate. Not to mention it could be a safety concern, ie an AP falling. 5 GHz as we know would be more impacted / not impacted by a mounting plate, if you take a peek at the attached, it appears the mounting plate is considered.