Originally Posted by
aastl
i fly with my dog all the time. he's a 10# cairn terrier mix. my experience has been that they weigh the pet in its kennel and may or may not do a visual inspection. if they do, it's cursory at most. i don't recall that they ever checked if he touched the sides of his kennel. happy flying.
It sounds like the guidelines are there to allow the employees to deny egregious cases (someone stuffing their poor animal into a clearly undersized carrier and/or playing the "he didn't fit so I had to take him out" card).
They're almost certainly not going to break out a set of calipers and meticulously measure the pet's clearance in all sitting and standing positions. If a reasonable person would agree that the animal "fits" into the carrier, I think OP is fine.