I am a lot more familiar with conventional keelboat rigging so I am sure others can add to or refute what I have to say, but it is my understanding that on a rotating mast the shrouds are not functioning to shape the mast but only to hold it up. The diamond stays along with downhaul and mainsheet will control mast shape/sail shape. So on the catamaran with rotating mast your shrouds need to be tight enough to keep the mast from falling off/flopping around and loose enough so that the mast can still rotate. So really shroud adjustment I would suppose is just a matter of how long you have your forestay set, but forestay tension is still controlled by the mainsheet. It sounds like you have yours about right. The only reasons I know to adjust them is that it can be advantageous in light air to have slightly looser shrouds so that downwind your mast can rake further forward or in a capsize if you extend a shroud on the side out of the water it can make recovery easier.

I think that too many people define rig tension as what they feel on the beach. They strum their forestay and say "Tight as a guitar string...Great!". This is useless and without merit when it comes to on-the-water tension.

We ALL have seen how the lee shroud flops when reaching. Less obvious but just as real is forestay sag when off the wind. No matter how tight it seems on the beach, under loads of sailing you only run on the two windward stays . Platform flex, mast stiffness, and mainsheet tension all add into the mix. I've heard repeated stories of people successfully sailing great distances with a lee shroud completely broken !

If you acknowledge that massive rig flexing loosens a lee stay, can anyone explain to me how "setting" rig tension relates to actual sailing conditions in any way?