Brooklyn and Prinz Eugen at the moment,... but it seems like balsa should not care what ship it’s mounted on? Spacing too far will add stress in the center of the gap.
It matters because you have to look at it from a ''where will i get shot?" perspective as well as how to support to balsa best.
So we are building our first Brooklyn... Looking at installing fiberglass ribs rather than making the hull sides super heavy. Then cutting will be easy and skeletal hull will be much stronger. Was going to go every 2” the full length. Where would you want them closer or spread out?
On cruisers (or ships without sidemounts in general) I'd recommend just evenly spacing them, especially for a first ship. KISS Sidemounts ships sometimes cluster ribs under sidemounts. And ships with a lot of bow freeboard and not much else target area cluster them in the bow. As long as you follow the spacing and total solid rules for whatever rules you're building to, do whatever makes you happy
For IRC rules ships get 15% length of hard area, which includes bow area, stern area, and ribs. Bow and stern max area total is 3” of length, so take 15% length, subtract 3”, divide by rib width, that gets number of ribs. Then to get spacing take length - 3, divide by number of ribs +1, that will give center to center spacing. For Brooklyn it looks like it should be about 2.5”