Structures all generating near spawn and clumped together

Hello, I've seem to have run into an issue.

I'm currently working on a mod with many structures, all of which spawn randomly throughout the world. However, after adding in the 12th or 13th, structure, I've noticed that it places every structure in the mod right next to spawn when creating  new world. And then from that point on, all structure become a very rare sight throughout the rest of the world. I've tried lowering the generation chance for every structure, to no changes. If you have any ideas to why or any suggestions, please let me know.

Regards and thanks in advance! :)