Every workout is moderate or hard to me. Nothing is easy unless it’s Pettit or less and nothing is more difficult than hard. So I’m always stuck levels 1-4.
I don’t mind lowering progression with ftp increase. But 5W ftp improvement shouldn’t take you from a 3.7 to a 1. Perhaps 3 would be better. If you were doing 15 min sweet spot at 235, it’s not that much harder if at all to do SS at 238