My take...
300m is too late to start a touchdown zone... If you flare slightly late, you'll get a touchdown prior to that, so pilots are always going to go for a gentle floated landing which we know hoovers available runway!
Second point is - If they want you to G/A at 600m then whatever. Play by their rules! Do it, keep your job... BUT! On really short runways 600m may well be too late, so always know your stop margin and if you haven't left yourself enough room then do the G/A before the 600m.