Have had some good results with the flexibility program.
Bit hard to explain all of the stretches, but the main (and most excruciating) involves the seated calf raise machine. Basically load it up, and one leg at a time sink your heel like the lowering part of the calf raise. For 15 seconds you let you heel continue to sink, even if you want to vomit. Then you hold the bar under pressure, push up for 5 seconds and let your heel sink again. Do this for three reps, three sets each leg. if it gets easier, add more weight.
Got the whole way down, butt to the floor, knees forward today squatting with plates under my heels. Soon I'll be able to do it without it. Not bad for someone with twisted achilles tendons!