Great, that's exactly what I'm talking about. Good use of the rook being adjacent to the king to control more flight squares. That's one of the strategies I thought of trying out.
If 47 is indeed the highest possible, then I believe we will solve this one.
I made two improvements. The first was gotten by putting the discovering rook diagonally adjacent to the king. This makes it much easier to guard flight squares therefore providing more freedom to other pieces. Here are 45 mates in one.
The other improvement was just making another line for a pawn promotion by moving some things around. Here are 46 mates in one.
All of the pieces still aren't coordinating well. I'm surprised that the solution isn't more than 47! Is it proven that 47 is the best solution?