Some observations—not opinions.
Randy Smith's SV 40 and Tempest 40 have 1/2" of asymmetry and the outboard flap is 1/8" wider at the tip—which on the SV 40, just happens to make the flap areas almost identical.
The Brodak Vector kit has the same 1/2" of asymmetry but the flap is not wider at the outboard tip—unless, as I have done with mine, you modify the flap blank.
The ARC/ARF Vector has symmetrical wings and flaps.
The Yatsenko Shark Ellipse has 24mm asymmetry but I don't know about the flaps. I will measure one if the weather is good at the weekend.
The Yatsenko Classic 2 has 30mm of asymmetry but again, I don't have any info on the flaps and we don't have one at our club so I will not see one for a couple of months.
There's no real question how this works or what the right answer might be, and that there is a range of asymmetry from 0 to around an inch that can be made to work. Statistical surveys on the topic on what various designers have done are vaguely interesting, but I am not sure what the point of it might be - its been documented in excruciating detail for around 50 years.
Additionally, people keep wanting to take a whole bunch of airplane "numbers", average them all together, and come up with the what is apparently the "correct" answer. The "correct" answer is not buried in statistical averages, and most of the airplanes designed aren't in any way optimized, nor is the performance, independent of the accuracy of construction, level of trim, powerplant used, evaluated well enough to give you much of an idea. The vast, vast majority of airplanes you see, including those finishing in high places at the NATs, are so "affected" by trim and power issues, that you really have no idea whether the underlying design is any good or not.
And in any case, just as an example, the optimal solution for a PA75 set up using Randy's instructions and the optimal solution for a PA75 using David's system aren't likely to be the same and certainly aren't optimal for a Saito 72, an ST60, or feedback electric system. So even if you use statistics to determine the "right numbers", you still haven't gotten anywhere.
People have known, to first and second approximation, what the "numbers" should be for a very long time now, and have a pretty good idea what things work with particular engine systems. But things that most people never even consider make a huge difference, and two extra swipes of sandpaper on the leading edge might make the difference between an airplane that stalls in round maneuvers at sea level air density, to a perfectly sound and reliably system that works at 105 degrees and 2200 feet.
Brett