Staff first names displayed in Teams

[sonofsanta]

In the realms of "minor issues I honestly wish I had time to deal with", but still. Our AD displayNames are set as Staff I Surname, and by and large Teams uses that for anything that happens in the channel. But! When there are collapsed replies, it decides to use the firstName field too, e.g.

Anyone know how to stop this? I don't want to overwrite the firstName field in AD with anything else, because if I use the initial there it'll be worse than useless ("S replied..."), because it's useful to be able to look up staff first names in a variety of differents places, and because there'll almost certainly be a knock-on consequence I can't imagine right now. I just need Teams to use displayName there instead of firstName, but I can't spot any policy or setting to achieve this. Anyone else had to field this complaint from staff and found a fix?