What you are doing is just fine.
Diluting coating simply allows you to coat into all spaces with a layer of coating without need for more powder. When excess Acetone evaporates, it leaves a thin coating which will dry more quickly.
Once thoroughly dry, then bake and repeat with the diluted mixture.
In most instances, any surface that does not come into contact with Barrel, really does not need coating. Coating hollow point inside hole is OK, but may be of no benefit.