I purchased your VG's a few months ago and this is the results of the test
This is a Kitfox 5 with a O200 continental engine both have 160 hours on them.
I installed as per-instructions with only a 3 mph improvement down from 48mph to 45.
So I modified the placement, and lowered the stall speed to power off stall of 41 and power on 34.
No stall just a sweet little dance and then flying again!
No difference in top airspeed of 100 mph
The forward VGs are 43mm back fro the L/E to the front tips, and the aft ones are 78mm back.
From the wingtip to the lift strut, the spacing is 60mm for both forward and aft ones.
From the lift strut to the wing root, the spacing is 60mm for the forward ones and 90mm for the aft ones
Bill, Washington USA. Kitfox series 5 owner.