Hi!
If you don't mind... what kind of bar(s) are you using the EZPZ with?
The Rivendell web-site displays it on an Albatross and on a Losco, I think. (Either of those could be wrong guesses.) In those shots it looks suitable enough to me. My setups have plenty of room: v-brakes, long headtube, tall quills, medium-to-long stems. So any challenge to the bag's stability/usefulness for me will likely be bar-related.
It's hard for me to see it working with a Moustache bar or even an Albastache. Though, should the stars align and SaddleSack production resume during my remaining years/weeks/hours, I do hope to find out first hand.
Yours,
Thomas Lynn Skean
who may "have a problem" regarding cotton canvas bags