RE: decoupling surfaces - mixing, or what?
Mixing will help, but it will not fix design characteristics. You can begin by 'estimating' the amount you need. If it pitches A LOT start with like 6% or less. Put the mix on a switch so you can turn it off. Some planes become un-flyable with bad mixing. From there it's trial and error.
No amount of mixing will make a plane 'PERFECT'. Your plane will never be completely 'un-coupled'. The closest are pattern planes and a few scale aerobats.