My thinnest self-adhesive felt, even with the plastic ribs round the inner rim obliterated, would be far too thick for this. I didn't even attempt it. Instead, I got my older paper-backed flocking and installed a strip of that. But it was a bit too thick as well, to my liking. My newest flocking is not paper-backed, hence thinner, but not by much. Still, I had no other choice...
It's quite snug, although I expect it to loosen up a little over time, but not too much I hope.
Thank goodness that's done.