On my first cabinet, I mounted the amp board to the underside of the control panel, only the knob was on top, in right upper corner out of the way. This worked out pretty good for me.
On my second cab I mounted it between the speakers, like you mentioned.
I did this to make the removal of the CP easier and less complicated.
This worked out better, IMHO. The knob is small, and above the screen, so you never even notice it. So my next two machines used the "between the speakers" method.