My vault recently hit 20 dwellers so I built a radio studio, assigned my 2 dwellers with the highest charisma to it and gave them clothing with charisma buff. After 1 day with the studio and no new dwellers I spent 1,500 caps to upgrade it to the radio station, and 2 days later still no dwellers. I know the station has only a percentage chance to find a new dweller, but after this long with high charisma dwellers running it and the upgrade I thought it would have found at least one dweller by now. Am I doing something wrong? Or is it just a really low chance of finding a dweller?