Hello,
I also use Al's flat tape process.
I usually lightly sandblast the untaped areas after masking and before priming so the primer gets good adhesion. I also use a "etch" primer. The same tape job works on the sandblasti and the painting. Be gentle.
The secret to a good job is to use just enough paint and primer to do the job. A very light coat of primer and just enough paint to cover is best. Heavy paint build up causes heavy, thick paint edges when the masking is removed.