The raised lip on the back is on purpose. It’s called the bi-level pocket, or something like that. It’s to keep the balls from flying out of the pocket when hit very hard. Diamond has had that since their beginning, I believe.
Interesting, never knew that. Other tables with truly flush pockets don't have issues with balls flying out of the pockets. I've seen people shoot into center pockets of a Diamond and it come out the opposite side pocket, on ball return tables. lol
I'd take the flush pockets over the chance a ball could come back up any day of the week haha. I've rarely played a set on a Diamond where that little lip doesn't cause some kind of issue for one player or another.