That's how we were always doing it as well.
Of course, because it is arbitrary, there can always be that lingering feeling that someone is getting unintentionally advantaged or disadvantaged, because the GM either lets them move too quick or too slow in their narrative approach to this part of combat. Fortunately, it's something that rarely actually springs to mind because everyone is more focused on pulling triggers and slitting throats.
Although there was that one time years ago when I played a DH1 Assassin that I felt I wouldn't actually get to make the most out of my character, simply because several of the Talents were relying on friggin' maps with accurate distance measurement.
In a way, it's almost the same problem with cover, although this is a lot easier to wing via houserules such as letting people do Perception or Agility rolls to check what sort of cover they manage to find in the heat of combat (and depending on the current environment, of course).