I think I've found a problem... Super-capitals are already the size of the moon and greater. The surface area of the moon is 3.793 × 107 km2, or 37,930,000 km2. North America, the size of my Dreadnoughts has an area of 24,709,000 km2. But that's only when flattened. If we make it 3D, the surface area of my Dreadnought would be close to, if not greater than, the moon's surface area. We have bigger ships, like Orph's, which are the size of Asia, which is 44,579,000 km2 in area. There is another set of ships that is the size of Eurasia, which is the combination of Europe and Asia together, summing up to 54,759,000 km2. Asia and Eurasia are already bigger than the moon, even when flat.
My suggestion is to make sub-titans the size of Earth, and titans the size of gas giants and bigger. Here's the current class sizes.
Fighter: F-16
Corvette: White House
Frigate: Downtown LA
Capital: New York
Super-capital: Continent
Titan: Planet-sized
Megalith: Sun to Solar System
The newer edition should be:
Fighter: F-16.
Corvette: Between fighter and frigate.
Frigate: Downtown LA to LA county.
Sub-capital (does not need to be requested to be made): Between frigate and capital.
Capital: New York to Alaska
Super-capital: Larger than capital to Eurasia.
Sub-titan: Between Super-capital and titan.
Titan: Earth to Jupiter.
Super-titan: Between titan and megalith.
Megalith: Mercury's orbit and bigger.