Shims are generally 10cm, which means only a cm below the bottom of the Kona weld. That may be just enough, but it would be better if it was a cm more. I think the point is that welding damages, as in permanently weakens, the area of the tube that has been heated. So a 9cm shim/post insertion creates an axis just at the point where the tube is weakest. 10cm may be ok, but only just.
Strangely, some Kona posts have min insertion marks at 15cm and some at 10cm. 15 seems way too much, whereas 10 may be only just enough.
Tom, I apologise for misleading you over the 27.0. The great Sheldon says 26.6 for both 94 and 95 Cinder Cones, but I had made a note that somebody had reported it was really 27.0. Clearly that was wrong and Sheldon is vindicated, not for the first time.