If heading that way, Mae Sot, may want to research Umphang Dist., Tak, especially if like 'the' waterfall, would think best in TH to see. They had a scam going, and why I never bothered. Insist you need a 4X4 to see, but can't use yours ... ????
Don't know if that's still going on or not, as was years ago when I was considering it. At the time, wife couldn't deal with another winding road in the cars we 'had'. Seems she has no problem in present car, and handled Nan with no problem, surprisingly. Mae Sot to Thi Lo Su, is 200 kms/4.5 hrs, nuff said.
Thi Lo Su Waterfall
Another negative, it's 1 road in, 1 road out, to & through Umphang.