So I have found that the rules from the Annual and the Abominable Intellect cards just don't cut it.
Making larger encounters with more baddies just results in longer games with little actual impact due to lack of space for them to reach the explorers or being left out of
LoS.
I've also found that the constant rolling/checking of the behavior tables slows down gameplay too much. Me and my group have agreed and have been using a set of rules that makes the game feel like a much better co-
op experience with the appropriate challenge we need.
I've compiled our house rules in my blog, for anyone interested:
Blackstone Fortress house-rules and custom behavior cards
I've also grown tired of endless behavior rolls and made a PDF with behavior cards that speed up the gameplay quite a lot. The PDF can be found on the same link above.
Let me know if you use these or have feedback, we haven't played any of the expansions yet and I'm going for a secdond run of the base game with these rules because we felt like it would be more enjoyable.