I was back home a couple of weeks ago and met up with my old group of mates 2-3 times.
There were seven of us, but arrived in drifts and drabs. The first four settled into one group (two rounds each) and the others stayed in as a threesome and had six beers. That's how we've always done it, and no-one takes the pi$$ as we all, bar one, drink bitter. The other one, a multi-millionaire, drinks that cold, fizzy, tasteless shite. And to his credit he always buys an extra round for everyone at the end (and not just to be flash) if they're up to it.