There are some sectors that are completely covered with radar rings, from multiple fields. Some sectors have, say the lower half of that sector completely covered within radar rings. If a plane were to fly from one sector, heading into another sector which is completely covered by radar rings, the plane would show up within the zone of the radars. So, what we see fairly often (and is very hard to show with a video, but we may have to try) is a red bar suddenly show up far into friendly (to us) bases, moving through sectors (the bar changes sectors) which are completely covered by radar rings, however there is no plane to be found. Then, just as suddenly, it will disappear, just vanish. It happens a lot on Titanic Tuesdays.