I saw something that gave me a new idea about the rosettes on the gap-sleeved tunic (Tunica mulbris). I’m sure someone else has come up with this theory but it was new to me. I was very excited when I stumbled across the image below. 

If these buttons were placed over the rosettes it would give the same look and provide the “button look” we see. while at the same time providing the gathered look and provides the gaps to be more… well, gap-y.

These wouldn’t be strong enough to hold the fabric but if the rosette was already made and these attached over them it wouldn’t be a problem. The upward point would also give room for the gathered fabric of the rosette.

The above photo is from Pompeii, around the time the buttons are dated to (see below).

Bracteate: Round gold “buttons” with a rounded (or pointed) dome and a bar across the back to attach them to clothing. Made in Afghanistan in the 1st century (CE?).