Honestly, I don't really know why Varroa don't seem to be a serious problem. Some of my strongest hives, 4 medium's full of brood, bees, and honey have managed to produce several frames with nearly all drone brood. I randomly opened some drone brood and open drone brood in nearly every hive I examine, but haven't yet found a Varroa in drone brood this season. I haven't "rolled" bees in anything to check for mites and haven't used a sticky board under SBB. I did see a mite on a newly emerging worker, it also had DWV. Their actually seem to be about 1% with DWV, so I am sure the mites are there. I have managed to get to where nearly every comb in brood areas are small-cell.
Some speculation has been made that our dryer, hotter, air might be the reason. I'm just glad that I haven't really had to worry so much about Varroa or TM.
You might consider my signature inaccurate if you consider small-cell a treatment, but when I first read about it, it simply sounded like a "fun" thing to do. I didn't actually see a Varroa problem that I hoped would be remedied by the small-cell. I like seeing the tinier cells and that makes beekeeping a little more, "fun" for me.