They come stock with (1) .3mm aluminum and (1) .1mm copper already installed. I installed one more .1mm copper shim for a total of .5mm to run 30%. I believe Drake had said on another forum that he runs them stock, which would be .4mm with 30%.
Running 20% or 25% you should be fine with the stock set up (.4mm).
I bought the promo kit before they started putting in extra restrictors. I run the stock which is 8mm I believe. Runtime doesn't seem to be an issue with this .28
Hope this helps.