Try to keep your film thickness down and work on your preparation...if your film thickness is thicker than the overall thickness of the tape, you'll end up with a solid layer of paint across your paint line, and no matter how good your adhesion is, you'll have a ragged edge. I personally perfer to keep my edge to less than two solid coats. Also, try to keep from putting on super 'heavy' coats, as the layer will sag up against the tape while curing and cause a huge 'lip' up against the tape edge, even if the tape pulls off cleanly. Make sure you're reducing your basecoats right and with the right speed of reducer for your temp, then put on two or three light/mist coats to get coverage rather than one solid 'wet' coat. You'll end up with the same coverage, but with less film thickness....
Post pics!!
Phil