my experience
I tighten the back stay to get the amount of mast bend I want, right now I have very little, could send a picture if you want. I then evenly tighten all side stays to be fairly tight and then go sailing in 15-20 knot winds. When hard on the wind I note how much slack there is in the leeward side stays and evenly tighten them so there is just a little slack. Not sure this is scientific, or the right way, but it seems to work for me. I'd like to have an adjustable back stay so I could change mast bend, but the geometry of the split back stay and my bimini means I'd have to take the bimini off, or somehow modify it. So far, I've not done this.
