spaced omnis
How far apart would you space your omnis? And how would you mike a grand in a small room?
As I said a few posts above, start at 50cm. That's where things usually sound best to me, but you can definitely adjust in and out by ear, and the Williams Stereophonic Zoom doc has a chart that can be helpful.
For a piano in a small room though, this is NOT a good recording choice. You're going to wind up accentuating all the early reflections of the low ceiling and narrow walls, and it will sound pretty awful. Piano in a small room means you really don't want much of the sound of the room in your recording. Instead, I'd try a traditional Faulkner array (20cm spaced fig8s, straight ahead) a little closer, maybe 3-4ft away and aimed inside the open lid roughly of to an angle at the bend of the piano. The nulls of the fig8 should help avoid a lot of those early reflections, except for directly behind the mics where you may need something absorptive on that wall opposite the mics.
Another option is near-spaced cards. I'd go for something like DIN or NOS instead of ORTF, again to reduce the room sound, but to give you some natural stereo. You could also go X/Y which would have the least ambiance, but I'm not a fan of that for piano because the stereo image can move around in a distracting way as the pianist moves up and down the range of the keyboard. In other words, the imaging is too precise. Same placement distance to start with, but don't be afraid to go closer to get more direct sound and less room. You'll have to experiment.
Just realizing that this should really be discussed in another thread, maybe in Team Classical.