The balls are the same for all shots. The cue is the same for all shots. The pockets are the same for all shots. Nothing changes with any of them from shot to shot. The only variable between shots is what you do.
If you hit the shot with top spin, but miss it with draw, you are changing more than just the tip position on the cue.
As someone pointed out, I can only assume that your fundamentals are not quite as rock solid as you believe they are. Something is changing with your stroke.
Steve
I agree. I probably dont hit the CB right exactly dead 100% on where i want to when i shot a long draw shot. on shorter easier shots they still go in. on a longer draw shot, that slight fluctuation causes me to miss.
Mike