Arne is much better at interpreting form videos than I am, so I'll leave that to him.
I tried fixed crawl for a while. The problem I had is that it requires much more discipline in keeping the bow vertical, or at least at a repeatable cant, than I care to devote to that particular issue. I vary my cant based on the bow I'm shooting that day, or just because I feel like it. Not much, just a couple of degrees, but enough to throw the arrow off when I'm using a fixed crawl. Other people, like longbow fanatic 1, tried it and really like it. The first I heard about it was Jimmy Blackmon's video, but he's way out of my class. Another person who's way out of my class is Rick Welch, who shoots 3 under with a nose anchor, like you and I do, and doesn't seem to be bothered by the big gaps. He's not a gap shooter, really, but he is aware of his sight picture, so his gaps are important to him in a subjective way.
Personally, if you have form issues, I'd advise you to work them out without using the fixed crawl, and I'm sure Arne would agree. The more variables you can eliminate when working out form issues, the faster you can work them out. It's really not important to hit your spot when working out form issues, and may actually detract from becoming aware of your movements. Fixed crawl is an aiming method, and can be mastered in a short time once your form is right.