I found this article very helpful in understanding some of what's going on with Ivan's hind feet right now. Apparently he may have developed the cross canter habit due to his heels being too low this whole time, and he has been constantly battling to stay balanced and comfortable due to his heels being dropped on the lateral side due to the way his foot loads. With a 2 degree wedge in the back, he now has enough heel on the lateral side to be more comfortable and take some of the strain off of his tendons in the hind, and this will hopefully cause his deep flexor to destress and loosen up because currently it's rather tight. This article had a lot of helpful information as to parts of the foot, function and relation to toe angle, etc. etc., and mentioned findings of small studies.
Heel Wedges: Their effects on Tendon and Ligament Strains
By Kent M. Thompson, PhD