I wanted to find out if I should put Psyonic Beams, Disruptors or Phasors VII on my ships. So I made an Excel sheet, searched the web and crunched some numbers. I the following site that explains the mechanics behind weapon size calculation: https://www.galciv.wikia.com/wiki/Miniaturization
With that, I did some calculating. I saw that weapon size is linked to hull size, using the size mod. Actual weapon size has nothing to do with the level of miniaturization. So here's an example.
The Psyonic Beam has a base size of 8 and a size mod of 4%. A medium hull has a size of 48. So the actual size on this hull type would be (8 + (0.04 * 48)), which is 8 + 1.92, which is 9.92. Round it up towards, and you have the actual size, 10. Then I look in the ship designer, and I see that it reports a size of 10.
So I checked it for Disruptors (actual size 6 + 1.92 = 7.92 -> 8), the ship designer reports 7. For Phasors VII it's 7 vs 6.
I then checked the large hull, but that was right as it should be.
So I'm a bit puzzled here. Can anyone clarify this?