Structure spawns within 128 blocks.

I've been doing some testing on quad witch huts, and found that even though my (afk) center point is 118 blocks away from each spawn spot nothing spawns. I maxed the sim distance to 10 and I've still had no spawns, 2 of the 4 huts will start working if i move 25 blocks closer. I'm just wondering if this is working as intended? Or a result of not having a sim 12.