BTW, Conrad, based on your smart comments, I did go and adjust text width for our widest breakpoint such that text width doesn’t exceed 760 pixels. Thanks for the tip! I’d been resisting doing that as I’ve mostly been trying to keep customization within each breakpoint to a minimum.
(And, honestly, I’d prefer a more “algorithmic” approach to styling in Adobe Muse, rather than having to do such things via a breakpoint. Seems like this is a common enough issue that text boxes [or perhaps paragraph styles] should have a “max width” setting, rather than having to change the behavior of a text box in the widest breakpoint. In my case, I handled this by setting the text boxes “no resize” with a fixed width 760 and center pinning them to the browser in our widest breakpoint. At 768 browser width and below, they “stretch to browser width.”)