I thought the Windex indicators were fixed. I don't know the angles but they are probably around 30. If as I suspect you are looking up the mast you won't be working to the last degree, but yes 30 seems the figure.
I am not familar with the boat but thought possibly the number 3 might go inside. For any sail that is outside I don't see how an inside track as one picture showed is going to work. Possibly on the number 3 the clew is high enough to clear the rails and be pulled in but that is going to hook the leech in which is not desirable as you want a clean runoff.
When I suggested trying an inhaul as an alternative, this was in the context of saying I suspected you could not sheet inside but if you could then it was a simpler alternative.
Some of the advice you were given was that you should be using an inside track and that the PO was an idiot.
"Inboard tracks are essential for racing - your PO was a dummy. The basic trim guideline for a 150% should be a few inches off the lower spreader - you won't get anywhere near that close with rail sheeting. It's even worse with a small jib
that you are trimming to the fattest part of the boat - you'll give away 5-10 degrees of pointing."
The sheeting angle in part depends on the boat. Clearly Giu has much wider decks, and I suspect comparatively smaller genoas which can be sheeted in tighter. Older boats have bigger overlaps and are often narrower and get more power from the genoa, so the scenarios are different.
I am no expert on wind tunnels etc. I imagine like anything else they have constraints but have proved useful. I suspect that people often overtrim, and confuse sideways force with forward drive, ie we are heeled right over so we must be going fast. Forward drive and VMG are what interests me.
Because there are many variables involved in trim for conditions, my feeling is that while knowing what adjustments you can make is part of the deal, often it comes down to listening to the boat and getting it to where it feels sweet, and the sails look right.
When you start adding in windshifts, current and tactics etc you see how fascinating it can become. Nothing like beating your mate by a second after a nail-biting finish when the lead has changed a few times over the race.
This is all part theory, part practical experience. That is why I suggested racing helps you learn even if you are in the tail end in a private battle with one or two others, because it gives you feedback and encourages you to try different things.