I agree with the bit about people keeping little fish in way to much space and big fish in not enough is stupid, which is why I will never own a shark or ray, no offence to those that do.
But I am a ferm believer in giving them alot of space, remember these fish are from the oceans, the largest bodies of water on the planet, so unless they are tank bred or raised, they will be used to alot more room. Now that being said, if you clown hosts something, they will not really leave said thing (be that a nem or LPS coral) so Clowns being a reasonably seditary fish could be fine. I just think its unfair to the fish for them to have to turn around after they swim a few body lenths.