I'm casting my mind back to ST with DS...
I remember him taking what felt like a long time to put himself to sleep in the cot. As long as he was calm in the cot, I stood back (or more accurately hid lying next to the cot or standing behind it!) and waited, only intervening (sh-hold) if he cried. I have a clear memory of watching him chatter to himself, kick his legs up, try to suck in his feet, wave his arms and legs around, thinking he's never going to sleep...then suddenly he would roll over, suck his lovey and switch off!
Once I knew this was what he did I started standing further away, then by the door, then outside the door. Probably kept this up a lot longer than I needed to, but he was my first and I couldn't really believe he was actually SS at long last!
Is it worth a try standing back once he's in the cot and calm and see what happens?