As of the current version (2.2/3.2), I feel like the Command Block within the Wither Storm Bowels can be heard from to far away as it can be heard when you are in another part of the Bowels, which seems off.
I suggest that the radius of the Command Block sound gets reduced to about 5-15 blocks.

Also, you should make it so that the Command Block can be heard everywhere in the Bowels once the boss fight has started.
I hope you consider this change.

Couldn't you just change this with a resource pack?

resource packs change sound files, not sound volumes. you can change what sound plays but not how loud or how far it can be heard.

You could use a resource pack to lower the sound volume with an audio editor.

You can use a resource pack to edit the sounds.json to decrease the attenuation distance (the distance the sound can be heard), however I do partially agree that the distance is a little bit too big.

agree it is annoying

Couldn't you just change this with a resource pack?

Will be implemented in the next major release