displacement sample rates for mr 1.5
 

I'm having troubles finding where I set the sampling rates for displacement maps when I'm using mental ray for rendering. I'm using maya 4.5. Anyways, when I change the settings on the attribute editor for the standard displacement, nothing happens when mr does the render. I seem to be stuck with some ultra crappy sampling rate. yet if I switch back to the default maya renderer, the settings work no problem.

So if I'm using mr to render, doi set the sampling rates somewhere else? or does the standard displacement shader not work in mr? Can someone tell me what I'm not doing corrctly? thanks for any help