I had the clutch inner replaced today. Noticed that when I put all the plates back in I had a tiny bit less clearance left on the splines then with the old clutch centre, so less for the pressure plate to engage on. Using a tyre tread measuring tool there now seems to be about 2mm for the pressure plate to engage on whereas before it was about 3mm. Could just be wear at the back of the old clutch centre I suppose.
Looks like the pressure would disengage from the splines when the clutch is pulled in.
https://s20.postimg.cc/70zcgftnx/SAM_0729.jpg