I don't have mine directly mounted to the wall or ceiling, but I took the liberty of commenting.
Perhaps a fabricated metal or wood plate(say 2"x4" with your choice of length) to extend from your secure wall studs locations to the Manfrotto EXPAN system.
(i.e. EXPAN system attach to your metal or wood plate, which attaches to your wall studs).
I know you don’t want AUTOPOLES, but I find they sure make things easy…
I know it isn’t the answer you asked for but, Pssst… AUTOPOLES - no screws, no plugs, no missed studs, no guesses; it facilitates background positioning in almost your exact desired location, just suction cups and a hinged/spring level for a very secure exact fit - no marks on ceiling nor walls and easily moved, if you want to change your background location. (installs in two minutes, even for a “height challenged” 5ft 2inch girl!)