no idea if the improved STS the OP is about is due to a wetting agent, but regardless I do think a wetting agent could be an improvement. even if it's just the ease of application(similar to adding flour to pollen, it doesn't increase the activity of the pollen as far as I know, but makes it much easier to handle, doesn't fly everywhere with just 1 breath).
btw, why are you saying plants aren't hydrophobic? the surface of leaves definitely is, you can see the raindrops rolling off in the rain, I also notice it while applying STS with a pipette. I have to do a bit of effort to get the drop balancing on a bud, and not make it too big, or it'll just roll off.
I think with a wetting agent I could apply it quicker, easier and have better coverage of the buds.
theory about the improved way of feminizing, maybe it's STS+GA3? I have to look into it some more, but on a quick search I found mentions that GA3 is involved in pollenproduction(quickly read trough the abstract of a paper looking at GA3-insensitive mutants in rice, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2217639/
) also, I've read about it here as alternatrive feminizing spray, so possibly combining it with sts yields better results as either alone? sts to block female expression, GA3 to stimulate male expression, leading to more viable pollen(and maybe better opening flowers) as sts alone?