A grand piano is no exactly point source. How does Atmos handle that? Can an instrument consist of multiple points? Like putting 3 mics around and into the piano and then call this three close point sources? Same for the drums: one point source for each single percussion instrument?
The simple answer is it doesn't.
You have two options the first is to record with a microphone array which matches the specifications for the location of the bed channels, generally 5.1.4 or 7.1.2 for atmos, and ship a bed only mix. This type of recording is welded to the Atmos speaker layout. For a description of someone doing this see:
https://www.resolutionmag.com/wp-co...n-Lindberg-Resolution-V19.6-Winter-2020-1.pdf
The second is to use an 2nd order ambisonic mic or mic array for example
https://www.core-sound.com/products/octomic
and render from that to the atmos bed channels. The advantage being you can render the original recording to any other layout you wish to in the future.
For studio produced atmos music you might use objects for capturing a performance in a space it would be bed only.