This issue has been tested and found in versions 1.19.4 and 1.20-pre4

The custom sounds in the resource pack constantly follow the player and maintain their initial volume while playing. For example, when using the playsound command to play vanilla sounds like minecraft:xxxxxx, there's no issue. However, when using the playsound command to play sounds from the resource pack, such as custom:bgm.01, they don't fade based on distance, even if more than 16 blocks away or farther.

Here's a simple resourcepack containing a custom audio file. is a stereo format. After using the command '/playsound test:bgm master @s', you'll notice that the sound doesn't fade with distance, even when exceeding 16 blocks.

After switching the audio file to mono, the issue was indeed resolved. So is this a feature or a bug?
I'd suggest adding an additional parameter to the playsound command to achieve a non-distance attenuating effect, for example: /playsound test:bgm master @s ~ ~ ~ 1 1 infinite
Instead of changing the audio file to stereo format.