As Steve says, displacing of radio aid symbols always happens when they can't be shown at their actual location due to other overlapping objects. We have no immediate plans to change the way these are linked with their actual position (it's always worked that way) but that would change given a consensus of feedback.Gas venting sites as with all airspace depiction will disappear when you are zoomed in to a very large scale (1:70000 approx). Such zoom scales are normally used around airfields when it's beneficial for the airspace to disappear in favour of greater ground-level detail.