When you're on the wire, your body weight is adding to the mast support. Keeping this in mind, I'll be adding an tenshionable/adjustable running stay to the wing.
I think it's usually not the case. When you are on the wire, the tension of the windward shroud is reduced. I think that only when your weight overcomes all the windward shroud tension -at which point you start tensioning the leeward shroud- you start adding more force on the mast base. But I think that doesn't happen in regular conditions, it's very clear when it happens because the mast moves windward and you see the shroud next to you getting loose, on my boat I've only seen that when somebody is on the wire being unnecessary (low wind).
To me the only factor that produces more down force on the mast base is the increased leverage, regardless if the person is hanging from the mast of from elsewhere. I don't see how would the additional stay help.
