This is interesting. I've been riding in them on and off for the last last 6 years like that with the thick part on the outside. I've been having lessons with a dressage instructor and my problem area is gripping with my knees as I have always done. She says using those treads the other way round will help put my legs in the correct place ie knees not clamped on and lower leg round the horse.
Oh well I guess the instructor must know, it's funny actually I ride with either mother and daughter in our village, mother is an A pony clubber, and daughter has evented at inter, mother says the feet soles out and daughter keeps turnign them so her soles are in (as your instructor said) maybe its just a good remedy?
Actually I used to clamp on a bit and it just took a lot of mind over matter and I got a bit better, I think regular fortnightly lessons helped too! I haven't a horse at the mo, (I'm just about to try one next wk)
Also reading a lot of classical lit helped too. I keep toddling off to put it into practice!
Oh yes, practice makes perfect and all that.. Trouble is, I've been a happy hacker for the last 10 yrs and previous to that riding for me involved everything other than dressage. This is all really new (and great fun) but the riding style is the opposite to everything I've ever learnt.