Generally I was always avoiding of wax....if u use wax..you have to be very carefful not to use too much and also not to touch any surface on the board during application. Even with wax I had expoxy inside the inserts in case by case...maybe i didnt use too much. I always thought that when heatpressing..may go outside...on the glass and epoxy resin and have bonding issues.
So I use tissue paper with tiny quantity of wax...pressed in the hole but not too much leaving air gaps ...as I am sure I will need to clean the insert hole whatever happens.
So use tissue paper as said,,,and leave epoxy get inside...no problem as you will clean it easily with dremmel wire brass brush....and the screw/insert is not damaged and it is quite fast....as the epoxied paper inside is very weak and in cases the woll think came out immedialy when cleaning it. Finally, there are inserts with caps on...but the outer inserts where so close in height to the top of the board that when sanding the core, were instantly untapped .
To find the inserts under carbon ...the best is to have the template/outline of the board and carefully find one by one. In my case ...since I use a heatpress I can see the inserts extruding micros of the top surface of board under light and can easily locate them. I tried the magnet inside the inserts once and didnt have such luck...as i wasn't sure where is exactly...but ok maybe I wasnt doing it right...and maybe tha caps/with glass/epoxy on top made the magnetic field weak....