There is no reason why Konas with different seat tubes should all take the same size post.
A 97 Cinder Cone seat tube has a 0.7mm wall thickness, so it isn't going to be able to take a 27.2 post unless it has been over-reamed (which is not unheard of).
The 95 Explosif actually uses a Columbus Max seat tube I believe, the only Kona ever to use that tube. The 96 and 97 Explosifs used round Columbus seat tubes, perhaps because low-band mechs were on their way (or maybe Columbus had run out of Max seat tubes, wouldn't surprise me). Either way, it was a 0.9/0.6/1.3 tube, the butting to 1.3 being external, hence the ED rising from 28.6 to 30.0. 28.6 less twice 0.6 = 27.4, so a 27.0 will fit easily and a 27.2 may fit.
Kona fitted 27.0 posts as standard, but sometimes they take some serious clamping to make them stay put in a 0.6 tube. Using copperslip rather than grease may help.