School Hall PA System

Hi, we have been asked to install a new PA system in our local school hall. The hall has a 4m ceiling height. How high should we mount FOH speakers, bearing in mind that the hall will be used for other purposes, ie ball games. We are planning on providing just two active speakers from the dB Opera Live range ( 350W each ) and placing them forward of the stage, on the wall. Would we be better flying them from the ceiling perhaps? Any advice welcome.