This is my second use of this simple projector mount setup I thought I would share. Last time I got pushback about its robustness. In actuality it was overkill before because the projector was very light (10#). Cumulatively I have used this setup for several years now and it's been a really nice clean installation. With this design it's only a 3/4" gap between the top (bottom) of the projector and the ceiling.
M4-stud mounted rare earth magnets: https://www.kjmagnetics.com/products.asp?cat=112
(these screw into mounting holes on PJ and there is enough thread length to accommodate a little roll and tilt). I used QTY (4) MM-C-16 which have 16mm diameter and 12# of pull force. So 48# total. I confirmed via the available gauss map that it would not affect the PJ electronics. They also offer MM-C-20 which has 28# of pull force, which is too much IMO. The Epson 5040 weighs 24lb so I have a safety factor of 2.0. You can always use more if you wanted, but I did not want to over-constrain the installation plane.
Threaded-stud knobs: https://www.mcmaster.com/catalog/125/2280
(these can mount into ceiling with a large washer on the other side to spread the load or directly into a ceiling anchor or stud, if needed. The one I used was here https://www.mcmaster.com/6079k15
and has a 1" diameter head, so when mating with the magnets I have quite a bit of yaw adjustment as well. Obviously make sure not to buy stainless which would not be magnetic
In my last application I also added a secondary safety cord using metal wire with about 6" of slack - in case the projector was bumped when working around it or it is hit with a ball (the only two credible failure scenarios). I did not do that here but it is probably best practice especially if you have kids.
Hope this helps someone!