I think having other visual cues and clues would help better than camera placement. Some ideas that'd be easy to implement would be
- shadows or ghosts on the walls (mimics the 2d view, but in the same 3d scene)
- have the ball transition in color/rotation/whathaveyou as it approaches: for example, red vs blue, and have it go red as it approaches player and blue against the computer.
- Have the ball leave a tail (easier to extrapolate visually where it's going, especially if the tail has perspective).
- Change the field of view of the camera, might exaggerate the perspective and make it easier to place it.
The grid is a great idea! I think it could look good, or adjusted even. Maybe make two orthogonal planes with some transparency that center on the ball?