I concede your point about the Momentum being smaller...however I have tested both the HD598 and HD600/650. To me, I believe the reviewer is correct. The ear pad hole feels larger on the HD600/650.
If you have access to HD558/598 and HD600/650...a dimensional comparison would be greatly appreciated. Since the ear pad holes are asymmetric for all models, two dimensions for each would
be preferred. I actually am interested in the HD598 in fact for its fun sound signature. But because of my big ears, I am more inclined to go with the HD600/650 because again my perception agrees with the link I provided.
So, if you could perform this dimensional comparison, it would be most helpful to those of us with bigger ears seeking a comfortable fit.