I have no idea. I'm really not sure there is a specific one that is going to be audited or whatever. It's not something I recall coming up in the risk management certification. My personal answer for what would be appropriate is about the "wingspan" of the average adult. If you want optionals to all be able to work on them at the same time, otherwise everyone is going to have to wait to do their straddle jump, etc. Not that anyone will ever actually go at the same time in my experience, but hey, in theory.