G'Day Spartan, I am not a plastering professional, but have just gone through plastering a whole bedroom, including a couple of areas where I joined pieces of gyprock that did not have recessed edges. I also sanded too far on these spots trying to get it smooth and exposed the tape. What I did, was layered the compound over a wider area on these joins which made the mound less noticeable. We know there is a mound there of course, but you cannot see it as the wider the compound is spread, the less the slope of the mound, if that makes sense
We have just painted the room with the undercoat/sealer and I am extremely happy with the result. There are no noticeable mounds or lines where any of the joins are.
Kev