It's not loudness. I had a similar experience with the V-80 on airplanes. It's almost like it amplifies the sound of the airplane noise. I swapped them out for my $50 Sony noise-cancelling IEMs to much MUCH better results than the V-80. The M-100s work pretty well for flying, though.
also why would the m-100 work better, they have vents just like the m-80s if anything bigger vents since the headphones full size... but it is over ear but i wouldn't think that would have THAT MUCH effect