In practice when do kiters start giving room then?
In practice, at least from my experience, if I need mark room, I will ask for it. I will give mark room if requested. On kiteboards (during summer) or skis/snowboards (during winter) races, we use up so little ground space that we can get close to one another that it is generally not a problem, the others will hear you and you will be heard. I have seen more than once where we were 4-5 racers rounding a mark within 1 or 2 seconds. There may be problems though when newbie racers do not know the rules or forget them in action.