We've just put a 2mm spacer in to offset the crank and things are much better. Still a very slight rub when in the 25t even after angling the cage a little.

I don't think this frame can be modified further. The tubing is too thick, then the carbon wrap adds to that.

Even if I recessed the tab it would cause the lower arm of the derailleur would hit the carbon lug before the limit screw.

So, on Mk2:
- thinner tubing
- recessed tab mount
- small area notched out of bamboo tubing below tab for derailleur arms to swing (done before carbon wrap), but would need to be done anyway as I would need to counter the depth of the recessed tab.

Also:
- thinner joins on the chain/seat stays (or further from axle) at the rear dropouts