The warps M to O are pretty much the same ores if not worse. I got to N from M and was so happy just to find that the money i got from 1 round of digging was actually less money then M. But i tryed hard by going back and digging at M and finally got to O only to find again it was even more less then N. I believe this seriously needs fixing.
Most of the mines have the same ores. It's not the total price that changes when you sell it, it's the price of one of the blocks.