[golfbulldog]

Correction: If one end of the clubshaft is pointing at the plane line, it doesn't guarantee that the clubshaft is on plane. For example the clubshaft could be under-plane or over-plane and be pointing at the plane line, and obviously not "on plane". (This after reading an article on GolfBetterProductions.com)

Isn't it , by TGM definition, still "on plane" if one end of the clubshaft is pointing at the plane line?

I agree that that plane may not be the most effective for your purpose and that a different plane angle may be more advisable - but it is still technically "on plane".