You don't use masking tape for paint edges... use 3M Blue or Red low tack paint mask.... comes in various widths... the red makes a tighter radious..... get it at any automotive paint store. Use the blue or red for the trim line only... then regular masking tape/paper up to blue/red tape for overspray protection. Use the base color as a sealer then spray the trim color with the lightest coats possible to get good coverage.... when it looks like it needs just one more coat... stop... you don't want a huge trim line ridge from excessive paint where the tape was.

P.S. - I often omit the sealer step if I am trimming a good smooth paint job(even fabric)... with the light coats... nothing ever runs under(unless there is a gap in the tape... seal coat dosn't help that) and you still get a very smooth edgeless trim line. Good luck.