You think there should be some distance on the books, but in point of fact the courts have already ruled in Arizona that you can’t put a set distance into law, not legally. The first amendment protects gathering news, which includes watching over the government, and any restrictions on the First Amendment have to be narrowly tailored to achieve their objectives. That is why we already have laws such as interference and obstruction. If you actually do something that prevents the cops from doing their job, it’s already a crime.
The other problem with the set number of feet failed laws is abuse by police. The cops will say they felt you were too close, and that gives them reasonable suspicion to detain you and possibly probable cause to arrest you. Even if video evidence later shows that you were far enough away, you already took the ride. And what happens when a cop moves toward you? If you don’t back up fast enough, arrested. Even if the cop has no reason to move toward you, and it looks like entrapment, too bad. You’ll have to prove your own innocence.