Custom ship design vs. premade chassis, space difference, bug?

Greetings

First of all, sorry if this is a common topic I just didn't found by searching the forum.. still too sleepy

Recently started playing Galactic Civilizations 2, Ultimate Editon, in particular v1.97 Twilight Of The Anmor..

And me found something weird..

When I build a ship and use one of the pregenerated hulls (which it fills automatically with my appropriate researched components) it's filled with much more than theoretically possible.

If I design one ship of the same size class myself, I can't squeeze anywhere near as much equipment in like the premade hull packs.

Same goes if me tries to rebuilt the exact same standard hull in the ship designer with the equipment the standard hull got filled with automatically: halfway down the road I have no more space on the hull left.

For example, a standard medium hull for beamy weapons comes with ~15 beam attack thingy while my design just gets somewhat around 7-8 attack strength, using the same weapon types and level and every other component.

So the question is: is that a known / fixable bug or am I just too stoopid?

/J