I think that you are right to pay attention to detail, I am lead to believe it is critical that the paint stops almost as the radius on the face ends, when I had mine done recently the sprayer just looked at me blank when I explained what I wanted and gave him the sketch, " ah we've done hundreds of these things and they have been ok" has anyone got the kit to actually if they are performing to spec????
If you do rub them down BE EXTRA CAREFUL!
You do right to pay attention to detail and give yourself the best chance - after all you could end up having the whole bumper cover sprayed if it goes wrong!!!