Is it possible that he already knows your preference, but may be teasing you (or even trying to scope out your reactions to find a preference?

I'd say that the choice of time/setting is down to whoever manages to end up poised upon a single knee first (which doesn't necessarily have to be the guy). Of course, there's nothing in the rules preventing the application of a few subtle hints, like a giant notice placed strategically where it cannot be missed, stating a preferred place & time...