You should read this study if you haven't already
We all treat different forms of achilles tendinitis and tendonosis. This landmark study uses loaded eccentrics and showed better tendon organization and decreased tendon thickness at follow up.
Tendons do seem to respond better to tension and loaded eccentrics certainly seems to do the job. Though, this study is 2004 and much new research has leaned us all more toward looking at pain free isometrics , in other words, taking that tension in a pain free single range load and helping the tendon to reestablish appropriate stiffness. Tension and time under pain free load is the key, then expanding from that into more dynamic load challenges like eccentrics. But, as always, it is finding the load your client can pain free tolerate, get the organism to reload the tissue without threat and then build durability and tissue tolerance to load.
"Conclusions: Ultrasonographic follow up of patients with mid-portion painful chronic Achilles tendinosis treated with eccentric calf muscle training showed a localised decrease in tendon thickness and a normalised tendon structure in most patients. Remaining structural tendon abnormalities seemed to be associated with residual pain in the tendon."
Ohberg L, Lorentzon R, Alfredson H, Maffulli N. Eccentric training in patients with chronic Achilles tendinosis: normalised tendon structure and decreased thickness at follow up. British Journal of Sports Medicine. 2004;38(1):8-11. doi:10.1136/bjsm.2001.000284.
link to abstract: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1724744/