Hello William, I have this doubt I cannot wait for another month. Suppose we have two identical tops, same thickness, same rigidity. Let's say they are clone of each other. One you build flat or with a slight arch on the lower face brace (as described in your book), the other one is built on a concave dish (I started to use one). Do you think you need the same bracing? Or, in other words, if you use the same bracing on the two tops, do you think you will get the same results? I am asking because I started to use a concave dish. I like the result better, but I suspect that the top is much stiffer this way and using the same bracing as built flat, will inhibit vibrations. I am not sure, but this is an aspect where I notice a difference. It might be one of those macroscopic aspects you were telling me.
It is very hard to answer your question in a helpful way. You're presupposing that there is a "good" stiffness opposed to a "bad" stiffness. But how do you ascertain or quantify those two? How do you predict or evaluate the results of the two? How can you be certain that the difference in sound is the result of that particular difference in construction? Do you know precisely how much stiffer the top becomes when you impart a "slight" dome to it? How would you measure that? How would you evaluate the results in a way that can facilitate a clear choice? In practical terms, the question is moot, unanswerable. There is no "tipping point", but shades of gray. You have to be very careful of assuming you may ultimately be able to master the "science" of something which is essentially a cultural artifact, that ultimately is to be evaluated subjectively.
The universal consensus is that the lower transversal needs to be slightly arched. It is a matter of opinion, however about the value of imparting a "dome" to the area below. I don't do that, so I cannot advocate or dismiss that technique. I'm not even sure how gluing the fans against a hollow form actually succeeds in doming the soundboard. Does it? Does it dome it more than just the residual dome resulting from the curved transversal? Does glueing together two elastic components while both are pushed against a curved surface impart a permanent curve into the results? How permanent? You would imagine it does. But...does it? Then, what results when the entire elastic assembly is subjected to 43 kilograms of string tension? What happens to your minuscule dome then?
Assuming it actually succeeds in doming the soundboard, you would imagine that the bridge would then have to be hollowed to conform to the curve--closely. Then you would also have to curve the bridge block used temporarily underneath the top to clamp the bridge to it while it's glued, in order not to disturb that careful dome. That means the bridge is now sitting higher than it would be on a flatter top. the fretboard inclination would have to account for that.
I'm too lazy to do all this, especially since the advantage of the extra work is inconclusive, or unprovable, and when too many world class guitars just aren't made that way. My philosophy is, also, that the simplest solution is more often the best solution.
But if you believe that the domed workboard gave you better results---go with it!!! Perhaps the dome thus imparted is interacting synergistically with some other aspect of your sequence and design that you may not be (and perhaps will never be) aware of. All you have, really is your belief. Or, you can fritter away your concentration imagining impossible scientific experiments that perhaps may illuminate the quandary. But I think that is an illusion. Those thought experiments (two perfectly cloned tops, one made one way, the other made the other way...which would be "better?") I can't image to be ultimately very productive.
Go with your belief. That is what is called intuition: following the path which you cannot prove will be successful before hand. And my experience is that your intuition gets better the more you exercise it. If you domed your last top and didn't "compensate" with the stiffness of the bracing--and the results were clearly positive--assume it was because of what you did differently, or at least know that you did no harm, so keep doing it and be content and turn to something else on the agenda. It is the habit of modern man to want to KNOW before proceeding. But you often cannot Know. And must proceed.
All I know is that my guitars became consistently successful--by the responses I get from clients--after making many of them--and relying on my intuition. Your initial success evidenced by the acceptance of your last guitar by a discerning musician, is the product of your trusting your instincts and then following them with persistence.