IMO sand will quickly work its way through the pad and fill in the underside of the plate.
I used a conventional setup. Not a reverse flow. I used 4 lift tubes with venturi power heads that each pushed about 300-350 GPH. I gravel washed by pressing through the substrate and pressing the bonded pad. Always got some detritus on each swipe but, nothing major.
Why not reverse flow, it is superior in every way no?