Thanks for explaining. The limits might have been there in original, it was 30 years ago I last played original Dune II :). By the way, when raising building limit, you have to raise All constants there, including slab indexes.
I made a mistake only raising soft and hard limit, then had all kinds of weird things happen when building structures in two bases, like wrong building being placed and so on. Raising slab and wall indexes by the same smount seem to work fine.