The argument for the Mouse.move() function requires an eight bit signed char (-127 to +127). Are resolution settings (say 1280x768) related to the -127 > argument > +127? Is it reasonable to say 1280/(127*2) = 5.04 pixels for 1 horizontal movement (i.e. Mouse.move(1,0)? Is the answer to this at the driver level?
Np. The mouse has no idea what the screen resolution is. Mouse movements are relative. The OS determines where the cursor should be, and then passes movement activity information to applications that have registered callbacks for the information.
