Do you mean you powder coated after sizing, or you tumble lubed in something like LLA after coating? You shouldn't have any reason to tumble lube powder coated bullets; part of the big advantage is they don't need any other lube, and don't leave any mess in the dies.
Sizing before coating is not ideal; some people do it but there's really no benefit, and the end product is not as good. Sizing after coating irons out any uneven spots in the coating, and makes every bullet the same size and round.
The airsoft pellets are also an unnecessary complication IME, since you have to pick each bullet out, instead of just dumping them out in the tray.
You aren't looking for a thick heavy coat of powder in one pass; two thin layers give better results with smaller defects. If you can't get an adequate powder layer, like my 2nd and 3rd pics in the OP (those are the second coat), you may be using a powder that's not ideal, or not shaking well enough. A gentle swirling around doesn't cut it, shake like you're trying to kill what's inside, for a good 20-30 seconds.
Last edited by Yondering; 06/12/15.
