I have many examples of the abbat/abbato/abbas/abbati/abbatis group of words (which are often abbreviated the same or nearly the same), but I didn't index them so it's difficult to find them in my files, but I located this one, which shows how the long macron runs horizontally through the ascenders.
The sample also has a vertical tilde, which I call the "squiggle" apostrophe, which I keep mentioning because there's a similar shape (with a few more wiggles) in a similar position on folio 1r of the VMS (this is an extremely common Latin abbreviation symbol):
The sample also has a vertical tilde, which I call the "squiggle" apostrophe, which I keep mentioning because there's a similar shape (with a few more wiggles) in a similar position on folio 1r of the VMS (this is an extremely common Latin abbreviation symbol):

