Adding to my earlier proposition:
If you do not escape from the opposite
end your fleet is effectively trapped in
space by the larger fleet (fleet bloackade/surrounded in 3D)? It would prevent you from moving your fleet strategically until you start a new battle and run through your enemies and out from the opposite side...
Larger blockading fleets ships could spread out from bottom to top before you had time to
exit from the opposite side (even if this fleets ships would be slower). This would make interesting battles where that sides forces who were trying to escape are forced to run through the other players battle line.
Maybe this sounds too far fetched, but hey, you can always try

.