Apparently (who knew?)the key to getting that classic draped dressage leg and deeper seat is to slightly weight the little toe instead of the big toe in the stirrup. I know it sounds too easy, but bear with me. Stand up and get in riding position and try it. Let the weight rest in the middle of your foot. Then weight the big toe. Then weight the little toe. Feel the different muscles the are engaged? Feel how when you weight the big toe your thighs would grip the saddle and your toes would turn out like this, taking your lower leg off the horse and your seat slightly out of the saddle?
Now slightly weight your little toe and feel how your ankle stabilizes, your seat deepens, the outsides of your thighs engage, and your whole leg becomes toned yet flexible. Draped in the perfect position around the horse. Like this.
Now go try this the next time you ride. Switch between big toe and little toe weighting and feel the difference in your leg shape and seat connection. If you want to add in an extra layer of goodness, occasionally slightly lift your little toes for a few strides without losing your stirrups and feel how that deepens your seat. I can’t believe I didn’t know this. Talk about a little change making a HUGE difference.