Define 'natural'. Do you want it to sound like what the piano sample set in use sounds like the original it was sampled from? What kind of sound are you really going for? What is the space you're trying to put the piano in? Jazz club, concert hall or what? There's no one set of eq settings that will work for all situations.
You don't say what eq plugin you're using. I'm not a big fan of eq'ing a piano because when I use a sampled instrument I use the best sounding one for the music at hand. Mostly some form of Steinway grand as I hate the harshness of Yamaha grands. If the track really needs the piano to be eq'd in broad strokes I'll go for the Dangerous Bax EQ plugin; elsewise I'll use the SPL Passeq. For really surgical eq I'll go with the bx_digital V3.
If you're using reverb that will have a drastic effect on the sound.
To use a bad pun you're going to have to play this one by ear
I've used the TCL2 on piano and depending on the music being played adjust the attack & release to suit. Try switching between the tube and solid state options. Actually my most recent compressor for piano has been SPL Iron.