I encourage those interested in what the effects of varied flap configurations will be to go on the AMA web site at this link--
https://library.modelaviation.com/search-by-title --and request to download the "Imitation" article, author's name "Fancher" from the September and October 1979 issues of Model Aviation. You'll have to wade through a lot of other stuff but there is extensive discussion of the use of different length flaps and the original airplane was configured to allow the use of flaps of three different lengths. You'll quickly see a a three view that makes the configurations clear and the articles spend considerable time discussing the very significant impacts of the various configurations.
The two articles are long and cover a lot of stunt ship factors but I think you'll be able to pick out the flap related parts reasonably quickly. Most of the "stuff" in the articles I'm still pretty sanguine about. Howard will (most likely...and accurately) find some of it technically short of a full deck in scientific terms but reasonably sound experimental practice was used in evaluating what the impact of the various parameters investigated were in the circle. You will likely note that at the time I was using 33% of the MAC as the approximate location of the "center of lift", a number gleaned from many previous articles that I had pretty much assumed were gospel...they weren't. Nowadays I think I'm more accurate when I use the 25% MAC approximation. This is a good example of an incorrect number that, in terms of evaluating the effects of things on flight performance, was of little consequence as the pragmatic nature of the evaluation was still reasonably sound.
Take a look, if you haven't read the articles before and I think they'll provide some insight with respect to flaps (their % of span, in particular).
The one thing I would stress is that I believe that lots of stunt flaps are way too broad in chord and, thus, create too great a hinge moment (increased difficulty in deflection under high loads) which is a huge factor in the dreaded Netzeband wall and, thus, increases the pilot muscle required to fly a corner. I don't see any need for the chord to be any greater than is necessary to allow the wing to develop the lift necessary in the hardest corners you're going to fly...plus a modest excess to account for higher density altitude situations than those in which you normally fly at your home field. The flaps on the Imitation were a constant 17% of the chord from root to tip and the airplane flew extremely well at up to 62 oz or more on a wing area in the low 600s.
Ted
Note: the link should take you directly to the "Search" page but after filling in the desired article/author, etc. a window will pop up in which you will have to use your AMA username and password to access the articles themselves.
Note 2: To save time, review the 09 (September) article first. It covers the lion's share of the design thought discussion. The October issue was more or less just another construction article.