Join Date: Dec 2010
Location: southern Arizona
What helped me was the description, "Let the weight flow uninterrupted into the heels". I have tight hips. The first 5-10 minutes of riding is trying to get loosened up so that my weight can flow around the horse and into my heels, without my thighs and knees interrupting the flow with an unintentional grip. It isn't that I try to squeeze with my knees. It is just I sometimes feel like I need to pry my knees apart, because my hips just naturally squeeze my thighs and knees.
The other terminology that helps me is to think of flexible heels ["relax the ankle joint" per the book above], not heels down or toes up. If my heel is flexible, and the weight is not interrupted by my knees (or thighs), then my heels will go as low as they are freely capable of going - and that is as far as they should go.
Riders ask "How?" Horsemen ask "Why?"