I don't know what you mean by heal stretch. Twice a day I sat on an exercise ball and rolled forward. The idea was to stretch my quad and bend my knee. Why? Because that was my one problem, bending. All the rest is a non-issue. Any other activity has the potential to set the stage for the scar tissue to re-establish itself. Not only that, any other activity will no doubt contribute to swelling, even if minor.
I would think by now you would see your ROM creeping up. In light of the fact that it is not, does it not seem prudent to focus your efforts on quad stretches/knee bending (still gentle)? Maybe you already are. My personal experience from having had arthrofibrosis is that the knee must rest except for targeted but limited bending efforts, at least until the knee starts bending more.