Yup, I quickly replaced the "nipple" on my pocket toted bottle with one slightly more slender to get it actually in the fill slot instead of just up to it.
I noticed this has been posted a couple of times that the M is harder to fill, is the fill hole that much smaller than the Air?
I've looked at the pics many have been so kind to post, but can't see the hole. (Again, maybe I could phrase that better)