I don't really like the Circle Island Fields are a sector and a half apart, thats to far. What is the map with the island in the middle, 3 Fields, 1 north, 1SE, 1 SW and VHs in towards the middle? I am not a big fan of that layout because it takes way to long to get to the middle of the island in a fighter. God forbid the fight is over one of the fields - you have to fly 2 or more sectors.
For your circle island, I would put the fields within the 4 sectors in the middle of the island. Make em all about 1/2 sector apart. Move the GV bases to the outside of the island, with spawns to their respective fields and directly to their towns for easy defense. Also create VH spawns into the middle of the island for a big Tank Battle.
Likewise on the long island I would make the VH spawns right to the city and one to the field for defense. Force the land grabbers to have to kill the Field VH and the supporting VH to take the base.
The other option you have is to reduce the size of the larger islands so you can get wider center islands to create the fronts mentioned in the earlier posts.
Just some thoughts.