yes, the problem in higher floors is not the rxlev, but rather the interferences : multiple sites will be received up there, it is almost certain that they will interfere with each other (since the frequency planning can’t take into account this situation : it will put too much constraints on finding a good frequency planning!)
putting an indoor site is a good solution only if you ensure the indoor cell is uing a clean frequency. Best way : provide a frequency band dedicated for indoor cells.
regards