In reply to:

The larger the space, the lesser an effect they will have.

SPL is king. No two ways about it. Regarless of room size. A person closer to any given sound source will hear it louder than a person further away. The only reason concussion grenades are more effective in smaller rooms is that you can only be so far away.

For example, I'm sure you could disorient quite a few people standing close together in an open field if you were to toss on in their midst.