Really there should be a way to just "do" this with RTT, I though max supported baking bump on a high as normal.... Well a quick way would be, apply your B/W bump map as a diffuse on the high, bake that down as a diffuse, then convert to normal and add to your baked normal, this way atleast it would like up correctly and…
A few times I have applied a simple surface bump to my high poly geometry, like a scratch tile, or a procedural dent map or a marble surface tile and been happy with the results, but unable to bake that material surface detail down to the low. I'm pretty sure max RTT can't do what I'm asking unless there is something I'm…