If this beam is carrying any load, I'd be worried. W10 x 12's are tiny and taking any cope out of them is serious, not to mention a top and bottom cope that has to accomodate an angle. Whenever possible, I prefer to connect shallower beams to deeper beams. Connection wise, you would be better off with a W8 x 10 or W8 x 15. This might avoid the bottom cope.