Ben was spot on with the repertoire comment. I have used the SF12 as the main mic on early classical stuff (Scarlatti, Bach, Mozart etc), but from mid-Beethoven on I prefer 1m spaced omnis (usually 4003) for the very reason that the imaging is not so precise.
I will put the "mains" 2 or 3m out (bisecting the lid/body angle as David suggested) and another pair out (usually Schoeps MK2S) about 6m and 3-4m high. In a really great room you can add another pair further out. Plush did this with a superb recording done in Carnegie Hall.
You cannot be in a great hurry with piano, but if you don't have time to tweak it is hard to go wrong with 1m spaced omnis 2-3m out.