I have an SF-24 here that I use on piano on a regular basis.... I don't often do solo piano with it as I'm more of a spaced omnis kind of guy when it comes to solo piano. However, for piano concerto performances I use it all the time- especially in Mid-Side.
The mic can tame even the worst pianos and a M-S spot on a soloist allows for a great control of width of a soloist.
If I were to use it for a solo piano recording, I'd probably use it in Blumlein as opposed to M-S and I'd probably start with it about 4-6 feet out and at about 8 feet high. Then I'd move to taste depending on the instrument, room and repertoire.