What Army doctrine/publication covers wear of the ceremonial belt (ASU)?

I would assume that the rules governing the belt are the same as other belts. Buckle centered on gig line, not cinched so tight as to affect the normal lay of the ASU coat. Now, as far as how "high" on the waist, and covering the last button vs between the bottom two buttons, I have seen it both ways on images. When I look at images of Honor Guards, it looks like the belt if worn at the narrowest part of the waist and falls between the two lowest buttons.

Perhaps reach out to the 3rd ID (The Old Guard) for guidance. I bet they have a POC on their website or FB page. Another place to look would be an Army Band unit.

SSG James Elmore, the only info I've ever been able to find on the ceremonial belt is from Marlow White. It's worn only with the ASU uniform on ceremonial occasions, with or without NCO sword or officer saber. The link provided is for the enlisted belt. Officers' belts utilize branch specific colors between the two gold bands along the outer edges of the belt. 1SG (Join to see) SSG Jordan Gaudard

https://www.marlowwhite.com/enlisted-army-ceremonial-belt

SSG James Elmore I searched the AR and DA Pam as well and couldn't find anything to help. What I found off a website was the wear is governed by local SOP. I did find another SM who wore the belt in his wedding a post on Rally Point. If you have specific questions, maybe that 1SG can answer.

Reference:
https://www.rallypoint.com/answers/asu-uniform-for-my-wedding