We get asked this a lot. Straight down, in a stable location above the bed, with the whole bed in view, with a little extra room to allow for pixel loss when correcting distortion is “best”. If your lid opens to a set and consistent location, mounting with the lid open works well for clearance and reduces the requirement for extreme fisheye.
With a well focused and calibrated camera, it is possible to correct an awful lot, but extreme angles or extreme fisheye will test the limits of it.
Mounting example:
