The large size Mag Float# 350 for glass should work fine for you, it is used for glass up to 5/8" of an inch.
The smaller sized ones won't work on glass as thick as yours.
I actually like the big magfloat, then use the 2 fishes nano mag for Detailing haha. Its smaller and gets in tighter spaces, also good for down near the sand bed so it doest whack my corals.