The fighter is set as low and still be visible as possible at .1. Huge is at the maximum without exceeding the hex. I tried it at larger but it looked bad when ships were around it.
the scales I used in the GalCiv3GraphicsDefs.xml were
<HullSizeTiny>0.1</HullSizeTiny>
<HullSizeSmall>0.2</HullSizeSmall>
<HullSizeMedium>0.4</HullSizeMedium>
<HullSizeLarge>0.7</HullSizeLarge>
<HullSizeHuge>1</HullSizeHuge>