Hi there
The start point is typically only configurable on the first slide where mouse movement begins. If you added a slide somewhere in the middle of a project where slides preceding this one have mouse movement, the start point is determined by where the mouse STOPPED on the slide just before this one.
If you wish to adjust the start point, duplicate this slide and remove all objects except the mouse. Then time both the mouse as well as the slide for .1 seconds. Then position the mouse where you want and ensure this slide is just before the slide where you want the mouse to begin in a new place.
Cheers... Rick 