I would scuff the whole panel, then pre-clean the panel, layout flames using 1/8th inch 3m blue fineline tape, then cover area thats not going to be painted, spray adheasion promotor in flame area, lay down flame color, pull tape soon like 10 min after baseing (it leaves a cleaner line), then blade my lines with a razor blade if needed, if you know how. I would then spray adhesion promotor over whole area and clear the whole panel.
Blading lines...take a razor blade, round off the edges with 400 grit, then rub the sharp edge over back and forth both ways on 400 grit, then make a handle on the upper edge of the blade with tape by wrapping around the none sharpened edge. Take the blade lay it flat with the paint holding on to the tape only and carefully move by sliding razor along the ruff edge. move very slowly only in the areas that have rough tape edges. This technique works wonders after a little practice and helps reduce the tape edge for clear build up.