I understand that, but that's not it. The damper is nowhere near the reed. It is definitely those little plates, I have now removed it and it is much better.
The sustain is now the same length as the adjacent note. It was wildly out of tune afterwords of course, but I moved the reed forward and got it smack bang on the note first time.
The second reed not so easy, had to move that bugger forward and back all the time to get it tuned.