13 mph = 17.71 feet per second. you need to scream from 30-40 feet away at that speed, to allow for a reaction and stopping if needed.
I don't ever see cyclists announce their presence in time to get a reaction and then stop in time. NEVER. However, I do it. Bailey helps when he's along for the ride. Most cyclists think saying it when alongside helps. That's absurd. This is the main reason for cyclists hitting pedestrians on my local bike paths. I have only once heard someone else even mention it on the internet.
It's often the cyclists fault for announcing late. I also see most drivers tailgating. It's just people, not just cyclists. It's frustrating. This is one reason many cyclists pass without making a sound too. Plenty of people go the wrong way when startled and even get mad. If you're going fast there's no time to say anything and be safe. I always see other cyclists in my mirror long before they say anything.

20 mph = 27.25 fps............If you yell from 15 feet away, it's much too late. Even 30 feet.
10mph = 13.63 fps.............20 feet might be OK. maybe.

Not understanding closing speed and reaction time seems to be the main reason cyclists complain here about peds, the bikes don't allow enough time for the peds to react and the bike to stop. And drivers about cars, bikes, peds etc.

I understand this and don't have close calls on a bike path, how odd.