i have only had one or two attacks at santuary in my current save (12 days time now)
1 at red rocket
a bazillion at the slog, warwick, and a few other farm heavy locations....
finch was attacked by ferals and the corpses never got removed and i never had another attack on that location or another attack by ferals anywhere else...
level 80+ super mutant attacks on somerville place are usually some of the most dangerous....
santuary only has enough food to support it, i doubled up on the water, it has crazy high defense and exactly 25 citizens.
sunshine tidings has 37 citizens, enough food and water to support it, nearly every working citizen is working on a salvage station.. that place gets attacked more often it seems.
warwick and the slog have 25 or so citizens each, over 100 food in both locations and warwick has 160 water. both come under attack pretty often, warwick is better defended by automated defenses and slog is 5 HE turrets + nearly everyone with a flamethrower, which the citizens looted themselves from all the times a provisioner getting attacked by the forged has called out the ENTIRE TOWN. however both have a defense rating just enough to stay 'green'. Warwick has 3 HLasers and a missile launcher but those only turn on with the siren. otherwise the settlement sits at 25 something defense... The Slog has only 46 defense, due to heavy turrets and a artillery cannon.
then there is somerville place... combined with defense over 200 or so and it still comes under attack despite not even having enough food and water to be self sufficient.