This is an age old problem that plagued FFXI and is still a problem in FFXIV, even with the advent of physics effects on armor (which don't seem to apply when sitting...)

Whenever you sit/squat/kneel/etc with these tipes of long length armors, they spread out and stretch in all directions around the character, and sort of hover/float between the legs in the front.

Armors like robes and the company overcoats are the worst. Get on a chocobo and you'll see what I mean. The bottom part of the robe/coat sticks way out in all directions, your arms clip through them and it just looks really bad. It's really annoying because many of these armors look great normally

The motions and poses could be adjusted to minimize this awkward behavior and clipping issues. When sitting, the rear of the robe/coat/etc should tuck under your behind, not flare out behind you.

Finally, the position that shields mount onto your model needs to be adjusted for many armors, with the shield clipping through the armor, especially while running.

These kinds of graphical problems should not exist in a game made in this day and age. I don't mean to sound disgruntled here, but this could really use some improvement. (I love the company coats, they look great even though they WTFcant have materia and dont have particularly great stats- they make you feel like you're in the military and they are compatible with all classes. The odd part of this issue is I expected the same sort of problem with the top part of the coats, but they actually bend in a reasonably appropriate way)

If anyone doesn't understand what I mean, I'd be happy to upload screenshots.