Ringleader

I have a question about Game play, I made this map that was about 1500km wide, and about 600km tall. Once you start out the map, and go into sensor manager, the edges of the map that are farthest away from you are cut out with because of some engine/distance problems, and the boundary that the sensor manager draws looks like a line that cuts out the map X/Y axis. If anyone has any suggestions on how to fix this, or if it cant be fixed, please let me know.