I would pinch the Salvia early on during the growing season to encourage more bushy growth. Could try that next year?
Don't know
about the butterfly bushes being so close to the Salvia with the same/similar color bloom.
Although, in the photo the butterfly bush does appear a bit more purple/blue, so maybe okay?
If the blooms were a different color it might make for a better photo op? I kind of like yellow or white against the blue Salvia (my personal preference).
That's all I have at the moment.