I'm no barman, but from what I observe when I order a pint of Sov. is that it has to be poured slowly, usually the bar staff will start the pour and then start another pint if different or go to the till, they will stop the pour on the Sov to let it settle a bit, sometimes even serving someone else. Then the pint is pulled. I like a pint with a decent head, so the question about top up is how do you want the head, more often than not, if it looks a bit low they will top up anyway, so by and large I have no complaints.