I sometimes find that if i tapped too hard to make a bullseye, it'll run past it. Just keep practicing. You'll eventually get it.
Also here's a tip. When working on a chip in the middle of the windshield, you'll not going to have the luxury of standing in front of the windshield and placing the injector right over the chip like you do when practicing at home. What I do is I'd place an awl through the injector and move it around until I hit the center of the chip and then I'll screw the injector down. I think somebody posted this before, but i'm not sure. Hope this helps.
