KK, you are right to challenge - it can be awkward and embarrassing but worth making the point - and you are brave, too. Any reactions from people who are challenged (by non-authority figures, fellow customers or passengers, people who aren't the proprietors, or even those who are duty bound or more apparently suitable to enforce face coverings, etc.) cannot always be accurately anticipated. Remember that people were spitting at bus drivers pre-Covid and it's still happening... If someone volunteers to move away, however, then you should probably say 'yes please' and thank them as they do so, maybe with a thumbs up.