Why do you think Fox recommends 15-20% sag for their forks? My guess is when you add too much sag to get a softer feel you actually end up riding a stiffer fork. When the sag is too soft you end up riding at the end of the stroke more often which with an air spring is going to feel stiffer because of progression. If you want a more plush feel set that fox fork around 20% so when you are riding the fork travel is more in the middle softer area when it bumps rather than more compressed and stiffer feeling.
I couldn't agree more with what you were saying. I think on a trail or enduro bike you can run up to 25% if you want a very plush ride. I am not sure why fox recomends 15 becuse imo that is just way to stiff. I do think it is all personal preference though. Thanks for The comment.