I use flaperons for flat spinning, but it needs to be the right %. The climbing flatspin (CFS) has to do a lot with the CG location. For the CFS the CG has to be quite on the aft side, which can compromise other flight behavior. Don't expect a rocket climbing. It would climb slowly. Be happy when you get a flatspin that just hangs there and doesn't loose altitude. Then work (giving more or less rudder or throttle for example) from there to see if you get it to climb.
As for the mixing goes, every plane is different, and requires more or less flaperons and/or spoilerns. A good starting point for me is 60% ! Then you experiment from there. Could be a little more, could also be less. Try the next flight with 70 or 80% and then the next with 50 or 40% only, and see which is the best flaperon rate for your plane, engine, prop, cg setup. You really have to dial your plane in. Could take a couple of flights.
I always like to set the CG on my profiles, so when flying inverted no or very little down elevator input is required. Once that is set, I work on my other setups such as flaperon and spoileron mix.
Hope this helps.