As a 1K on a B fare, I’d think that you have an excellent chance if there are really any op-ups. However, some passengers may mis-connect at FRA; others may have last-minute changes of plans; etc.

I would fully expect the UA agents in Germany to follow the specific rules for op-ups. They will start to move people prior to boarding if they aren’t waiting for any connectors / last-minute stragglers, etc. Otherwise, they would go on board and move you. You can certainly delay boarding if you want, but if you’re thinking that UA agents will be deciding who to upgrade by looking around the gate area — that doesn’t sound like something that I’d expect to see, particularly in that particular location.