The short answer to your question is, "No." You can't trust your horse to self-regulate because horses are horses and they defy logic!
All joking aside, this formula (free choice feeding IR-leptin resistance (LR)) seems destined to fail more than most.
I too, have trouble with Getty's over-generalization and over-simplification of leptin resistance. To be sure, excessive forage restriction can be as harmful as free choice but there is no reason to go from one extreme to the other - all things in moderation. Feeding 1.5% - 2.0% body weight (or better yet, feed according to calorie needs and calories in your hay!) is moderate and I wouldn't consider that to be "restriction."
So, before I would hang my hat on free choice feeding as the solution to IR/LR, I would turn to the very best, most effective, least expensive, simply miraculous, amazing, appetite reducing method that (even more amazing) everyone agrees on (wow!) and that is...
....wait for it...
Kathleen (KFG in KCMO
Director and Research Advisor, ECIR Inc.
Dec 2005 - Missouri, USA