Anyone know how to set up an Envy for 80% letoff?

I've heard you should move the draw module to 1/2 inch less, then move the draw stop to get 80%. I imagine the net change in draw length is 1/4 inch or something like that. I've also heard that the Envy draw lengths are a little long, so if I actually want 29", the 28.5" setting might be right on.

Am I close to right?