I tried my Eotech 552 Holosight both on top of the carry handle and over the handguards using an ARMS #39 A2 Plus mount.
I'd recommend getting it as close to the height of the regular sights (2.6", IIRC) as possible to minimize deviation from zero at various distances. As the Eotech (and Bushnell) Holosights are pretty high already, the only way to do this is to mount over the handguards (or on a flattop.)
It wasn't unusable perched up there on the carry handle (and would probably be OK for indoor/house distances), but I didn't like it for 50-100yd stuff.
If these online ballistic calculators are reasonably accurate, you'd be looking at raising POI 3.5" to 10" at 50 and 100yds, respectively (25yd zero.) I would have guessed 2-6" from my limited range experience with this configuration, so YMMV.