I can't say this as fact, but I've been searching and the consensus is that the higher your defense stat is, relative to your food and water, the less chance that you will be attacked. After playing more hours than I care to admit (I have around 15 settlements), I think what I've been reading is accurate.

Realistically, it makes sense. I sure as hell wouldn't attack any of my settlements (I'd be dead in a second). As far as gameplay goes, this is extremely disappointing. I didn't spend hours gathering resources and meticulously placing turrets so they would never be used. That makes no sense. I might as well place 20 turrets in the middle of the settlement and move on.

I really had hoped that this would be the opposite. As your defenses raise attackers should be stronger.

If this is all misinformation please let me know. For now I guess i'll just plant a redundant amount of food.

If anyone knows other ways to increase your chances of being attacked please share.