Well, the pouches arrived. I am a bit disappointed, as they don't fit as it looked like they would. Whoever measured them for the ad must have included straps, buckles, etc in their measurements, because a depth x 2 + width x 2 far exceeded the bottle diameter x pi.
I forced a bottle in, took several minutes of effort. You can't tell but that pouch is stretched really
I am hoping there is some give in the fabric, because otherwise, insertion is a one-time thing. I'll leave the bottle in overnight, see if it loosens up. If that doesn't work, I'll try soaking it in water (works with new boots).
I guess I could remove the pouch to fill the bottle, rather than removing the bottle from the pouch.
Other option is to cut and sew in an elastic panel. Wife could do that pretty easily, but I hope it isn't necessary, especially since elastic relaxes over time.