I find >16mm comfortable, sometimes I have to push my eyeglass lense closer to my eye and have it touching the EP eyeguard to get the full FOV.
To this end I've ended up saving and acquiring long ER such as Pentax XW.
Personally I prefer to just leave my glasses on due to astigmatism and being able to look at the sky then move to the eyepiece, besides, no chance of getting your eyelash oil on the EP with your glasses in the way
.