So I just reached level 11 and have people at 2 of the settlements (Sanctuary and AF). I stopped the people at Sanctuary at 7 just because I wanted to wait on getting a ton of people there, and just have the 3 at AF. I've only had the mini quest at AF to defend it but not had any other raids. Does it happen more often at higher number of people or level? I do know about the defense mechanic for lowering raids. So was wondering if there is a trigger number of settlers or something before attacks can even happen?