Welcome to the forum board.  Unfortunately, I may not be able to give you the quick fix answer you're hoping for. 

  Time and temperature of the cure should have no real bearing on the amount or orange peel you see in the finish.  Orange peel is, as you correctly stated, due to thickness.  There are really only two ways to address the issue.  The first is to get with your powder manufacturer and ask about their low film/low orange peel finishes.  Many powder companies now have a specialized line that is designed for lower orange peel.  If you have no luck there, try comparing the specific gravity of the powder you are using to a similar color.  Finding the one with the lowest specific gravity (generally speaking) should mean that it will cover at a lower film rate because it probably contains more pigment.

   Maybe this will get you started.  Best of luck with your coating projects!

Joey