Servers that also pull manager shifts

My question is for those of you that have servers that also have manager on duty shifts.

I am curious how you compensate them In the case that you are short handed and they are the MOD while serving ? (Ie; instead of strictly being the manager on duty, they have to take section at the same time. Open the store, count drawers and run the shift while serving including performing all side work)
Are they clocking in as a server because they are earning tips? Or are they clocking in as a manager because they are performing both jobs functions?

I don’t have seating, so my answer would be more in theory than practicality, but I have mangers who work shifts as inside employees, or delivery drivers. When they do so they are still getting paid their manager pay, although caveat being that drivers get paid a separate on the road rate that is the same across the board (our tipped wage).

I would pay them the manger wage, because they are still responsible for every bit of the manager work, but add the server rate on to it. It is a small price to keep a good employee happy, and prevent losing them to the competition.