Playground safety zones are that space around the equipment installed and being used, where it is most probable a child will impact in the event of a fall. Generally, this is 6 feet away from all structures, except with certain types of equipment where this distance is increased and / or cannot be overlapped with the safety zone of another piece of equipment. If the safety zone is too short, the obvious likely result is a child will impact any apparatus or border placed within this safety zone, not the fall impact safety surfacing installed. So it almost doesn't even matter what kind of safety surface is selected if the proper safety zone isn't observed. 

Older children are more likely to impact further away from structures than younger kids, and they normally reach greater fall heights (especially when using equipment in unintended ways). Yes, playing "king of the hill" or variations of it are still present on playgrounds, where the maximum fall height becomes the top of the roof of an elevated playhouse. This is the real height that must be considered when comparing different safety surfaces and their respective HIC scores at 17 feet (maximum fall height which can be tested and compared under ASTM F1292). 

In short, equipment where safety zones cannot overlap the safety zone of any apparatus involves those that either move or create movement of a child through it's intended use, such as a teeter totter or something similar, in contrast to stationary equipment. Slides should add the difference in elevation between the highest and lowest seating position to the standard 6 foot safety zone, extending it to allow for forward motion at the end of the slide and greater possible landing zone. For swings, creating a suitable safety zone involves doubling in each direction of the swing's normal motion the measurement from the pivot point at the top, to either the base of the seat or the top of the safety surfacing, depending on whether the swings are intended for older or younger children, respectively.