Introduction

Let's start with some basics.

First off, size scaling in Star Ruler 2 is not linear. If you double the size of a ship, the actual in-game size does not also double. Instead a formula is used that infinitely increases in-game size but at an every diminishing rate from what it would be if linear. The reason for this is because the scale of things gets radically out of control if you attempted to keep it linear. DOF does adjust this algorithm from the stock game though.

Stock doubling of size = x1.32 bigger visually
DOF doubling of size = x1.51 bigger visually

DOF also halves the total size, so size 1 ships are effectively size 0.5 visually but its rate of visual size gain is faster so ships quickly become larger in visual scale than the stock game too.

DOF also assumes that Size equates to diameter (or length) of a ship in meters.

Here's a quick comparison of ship sizes stock vs DOF

So, as you can see, there is a much greater visual disparity between small ships and large ships in DOF. Visually, a size 32 ship is x8 larger than a size 1 ship in DOF where as in the stock games it's x4. A size 2048 ship is ~x97 larger than a size 1 in DOF vs ~x21.1 in stock.

Planets & Stars

Stars and Planets have been adjusted in DOF to use a similar sizing scale as ships, but scaled down by a linear margin. Planets are at 1/20th scale and stars are at around a 1/50th scale (with a caveat).

Earth has a radius of 3,185,500 meters. If we apply the scaling algorithm to it's diameter, it comes out to ~3990 radius. At 1/20th scale that becomes ~200 radius in-game. Mercury works out to ~112 radius. Saturn ~456 radius. Jupiter ~713 radius. Planet sizes in DOF are currently set to 60-300 radius.

The Sun has a radius of 348,171,000 meters. That gives us a base in-game radius of 66687.52. With a 1/50th scaling applied, it becomes 1333.75 radius. DOF stars are currently set to 550-2000 radius. Now, the Sun is not a very large star in the scheme of things. Betelgeuse is a massive star and even with 1/50th scaling it would have to be 98500 radius in-game. That's not really feasible so stars in DOF are all of the smaller variety, even if scaled based on real-life sizes.

Why are planets and stars scaled at 1/x instead of left full size?

As cool as I think that would be, there are several issues with it.

It would make solar systems and galaxies much, MUCH larger. DOF systems are already something like x6 - x8 larger than in the stock game. System spacing is x20 larger. If stars were x50 larger, those values would most likely have to increase by at least the same amount - possibly more to look right visually. I'm not sure what the engine's limits are for zoom distances and whatnot, but I'm not sure that it would be feasible.

Secondly, there are gameplay reasons. In order to keep the "feel" of play similar to stock, travel speeds, weapon speeds, ranges, etc would also have to be adjusted. It wouldn't work to multiply them all in a x50 manner as some things would get a bit absurd. If you were to attempt to scale things properly, it would probably be best to shift a lot of that stuff to a more simulation type of values. As cool as that might be, it wouldn't feel like the same game at all and most popular Sci-Fi is not based on actual realism.

Given the above, I maybe wouldn't mind trying but DOF is intended to be a "game" and not a simulation. It would be best done in another mod.