Hi ...blusnapper.
Look in the settings icon (top right of screen..3 gear wheels ) and the 5th line down.
"Map Safe Area Radius" and change it to say 600 m...or even 1000m
Mine version ( latest ) lets me change this setting.
The reason for this red circle , around the area you are flying , when you zoom down in the map screen, is a "warning" on how far you are flying away from the transmitter and is asking you to be aware that you are going out further if you change from the original setting of 500m
I have not reached this red line yet...so I guess it is a safe guard to not allow you to go too far away from your intended mission.
I will also try this maybe tomorrow and let you know.
The crops I fly over are 800m in diameter and I only fly to the center radius...eg 400m so I would not have seen this issue come up ...yet.
...Pete
some where I read that it will stop your aircraft passing the line...you can't go any further than the red line...where ever you set the Map Safe Area Radius to.....I am unsure , until I try it out myself.