in case some data might help others, here's my PMC from May 1st. I didn't have a good spring, either, so by May 1st I'd dropped my FTP to 260w. Note this was a very rough estimate just based on experience, and it may have had no basis in reality. It would be a few months before I could garner the motivation to do any longer intervals.
The subsequent adjustments to 250w, 240w, 245w, were also untested. In retrospect, I probably never dipped down to 240w, but since an injury was involved I felt better erring on the "safe" side, as I mentioned in my other post. I had a decent August, and then after a rest week I finally felt motivated to do a CP20 test, from which I estimated my current FTP of 265w.
Bottom line is I'd suggest dropping somewhere between shovel's 10w suggestion, and 10% of whatever your pre-injury FTP was.
Good luck!