When going through some of the Desktop Tuesdays, I found out a few things about the spawning distance. It’s based on a shape of the outermost pieces of your buildings (for example, actual buildings, zones, stockpiles, etc.) and then given a distance from that area. By my playthroughs as of right now it looks to be 50 blocks, seeing as a goblin camp just spawned a short ways away from my housing area. Attached image for reference:
Unfortunately, as also shown in the image, it looks like items placed such as stone braziers and fire pits are not
included when calculating areas that monsters can spawn in. Which kinda sucks. I just put a bunch down thinking it would.