Looking very close, there are some extended corners on the square tabs.
Each tab was stood on end and the small extended corners cut square.
The laser burned sides were sanded and cleaned up a bit with 400 grit on a block.
Not much glue was used, I didn't was glue to ooze out to the sides.
The tabs were set in place checking both sides to be sure they were even.
After checking the fit on the body tube, the tabs were just a little too thick. This raised the root edge above the body tube slightly.
This required a little sanding of the tabs down to and even with the root edge
The fin on the left shows the thick tabs. The fin on the right is the tabs sanded flush with the root edge.
EDIT: I was sent some great IRIS scale information from Massrokit, a TRF member.
From the closeup pictures of the real IRIS, the root edges of the fins don't make contact with the mainframe body. The only attachement points are the fin tabs and rear band.
So with the Semroc supplied fin tabs being a little high, they could actually "raise" the fins away from the body tube. For me, this wouldn't give a strong enough root edge joint. Still, an interesting twist.