Opportunist

Is there a way to tell how much coverage a field generator covers before/after you place it? I don't know what sizes to place to cover my ship. When I select the block it turns my whole ship blue immediately regardless of the size of the generator block which doesn't seem right. It is all blue even with a .5x.5 block. My ship is around 6mill m3 with all its armor removed if that is relevant. Any guidance would be appreciated.