I did a test once using automotive striping tape on a 100" sailplane with a E-205 airfoil.

I first put a strip on the right wing at 25% then launched. The sailplane went straight up on tow, but after coming off tow it slightly turned left.

Next I put one strip at 10% on the left wing. On tow the plane pull slightly to the right, then it turned slightly to the left after coming off tow.

I then put a strip at 10% on the right wing. It launched straight, then turn slightly left after coming off tow.

I then add a stripe at 25% on the left wing. The plane launched straight and flew straight.

I concluded that the 10% strip was working at High CL, and the 25% was working at lower CLs.