My experience with these powders is that it doesn't take a whole lot to get the job done. In a clear acrylic I am guessing that you are looking to top coat a base color. If such is the case, I'd spray several patched of the base color on a cardboard surface and allow them to dry, then I'd start adding the powder to the clear in small steps and trial a shot after each addition until you get what you are looking for as far as coverage and effect. I'd be fairly specific on the powder additions to a specified amount of the clear paint and write down everything so it can be duplicated at a later date.