I found it difficult to attach flatbands TTF to a narrow-forked slingshot, because the flatband would be pinched out of shape by the rubber band securing it, because the fork is made with a gap for use with tubes. The gap/slit is the problem.
My daddy used to say, "Son (he called me "son" - I didn't have a name until he was sure I wasn't a girl), as you go through life, remember that your main purpose is to fill as many gaps as possible".
Pursuing that advice, it became apparent that if I filled the gap/slit on each fork, the rubber band would have more surface area to secure the flatband properly.
I'll attempt to attach a few images to demonstrate that after all, daddy was right.