I too think that ring flutter is not what was being experienced but it was valve float.

Ring flutter is usually some combination of stroke (resultant piston speed) and rpm. This also has other variables such as the cross section of the ring and the resultant harmonic frequency of the ring. When everything matches, you have flutter and resultant lose of power and increased oil consumption.

It baffles me as to how one would be so positive about the presence of flutter?

Jim