Deep and resonant with less sharpness sounds like you want to put the mic underneath the piano pointing up at the sound board. You'll probably want to move it around down there and experiment with how it sounds in different places pointed towards different parts of the sound board. I'd start off pointed toward the bridge in the middle of the board, approximately.
You probably won't want it too close to the pedals, and definitely not too close to the ground. You might experiement with the piano open versus closed. I would guess closed will sound better but I've never tried it.
If you decide that's too muffled or you want a more complete piano sound, I would open the top to full stick and have someone play the piano while you walk around the open side of the lid listening for the best sound. Also try crouching and standing on tip toes to see how that changes the sound. Then put the mic there but move it a bit closer, since your ears will naturally minimize the amount of room sound you perceive but the mic will not.
The ultimate answer for where to put a mic is always where it sounds best. Ideally you would have a separate control room with speakers to listen through while someone plays the piano and your assistant is moving the mic around for you while you listen for the best spot. Back in the real world, if you have headphones or in-ear monitors with decent isolation and someone else who can play for you, you can find good placement that way. Worst case, you can guess at placement, make a short test recording, move the mic, repeat, etc. Or if you have a player you can have them play and record while moving the mic around the room and keep a record of where it is at what parts of the recording.
That last paragraph applies for micing anything with any mic.