If your framepainter can't achieve what you're looking for I doubt a bunch of us yahoos on teh internetz are going to be of much help, but what the hell, I'll add to the noise.

When I was doing "candy apple" finishes on model cars 40-something years ago the base layer had to be a dense metal-flake silver or gold. Lots of metal flakes, uniform sized, not too big but dense-packed so you got a consistent even distribution of flake. Almost looked like sandpaper when it dried. But highly reflective sandpaper. And then the top color coats were almost translucent...very thin, only slightly more saturated than a tinted clear. And you had to put several coats of that topcoat on before it started to look like shiny glossy candy.

So that's what I would do if I wanted a candy apple red bike frame. Although I wouldn't trust myself to do that job nowadays, I'd turn it over to a real professional.

Perhaps ironically, the bike frame I own with the most iridescent depth, just incredible 3D metal flaky luster that really pops in sunlight...was powdercoated.