It is thinking about Stainer's instruments from the point of view of mechanical waves propagation that I get a new explanation of how string instruments work. Using this physical principle I also understand why instruments with lower archings produce a clearer and more direct sound than instruments with high archings.
Jakob Stainer was a violin maker from the XVII century born in Absam, in the Austrian Tirol. He was the most appreciate violin maker ever until somewhere in the XIX century. Walter Senn and Karl Roy explain in their book "Jakob Stainer" (Ed. E. Bochinsky, 1986) that Bach and even Corelli had Stainer instruments. The fact that Corelli had a Stainer and not an italian instrument is very significant: it was easier for him to get an Amati than a Stainer, and still he chose Tirol instead of Cremona. It is not surprising then that Stainer instruments, as Senn and Roy explain, were in that time ten times more expensive than italian instruments.
Leopold Mozart wrote in his violin method that compared to the "German" violins (Stainer's), Italian instruments (Stradivari's, Guarneri's, Amati's) were rough, not very refined. He explains there too that it was common knowledge that the blades of a violin had more wood in the middle that in the edges, what suggests that the difference of thickness were big enough to be seen with the eye, not as the difference in the blades of modern instruments.
I have found musical and instrumental reasons to prefer Stainer: being myself a viola player, I always found playing chords on a modern instrument most difficult. Being the music of that time full of chords (think only of Bach's solo violin sonatas and partitas) one wonders whether in that time they liked to have a difficult life. But when mounting a Stradivari bridge on a modern instrument, it becomes more sensitive and gains in sustain. Mechanical waves propagation shows that the very concept lying on Stradivari bridges is applied by Stainer to his entire instruments. Then the question raises: how more sensitive were and how much more sustain did Stainer's instruments have before being transformed?
So it is not that musicians of that time loved having it very difficult. Instead, it is that the "language" that musical instruments spoke before being transformed in the XIX century is the same language in which those musical texts are written.
From the feet of the bridge, mechanical waves produced by the vibration of the strings enter the front of the instrument, and from the front they go to the back, first through the sound post, second through the ribs.
This lower position of the bridge suits very well the baroque instrument for two reasons. First, regarding the shorter neck of the baroque instrument, because the length of the strings is in this way conserved. A shorter neck solves the problem of going down to the low positions, because with such a neck you can go down to the first one with just one strike of the wrist.
Second, because that lower position of the bridge, regarding mechanical wave's propagation, unifies the concept on both halves of the instrument.
Unfortunately those edges have disappeared from some Stainer instruments that have reached our days. Some say that with the years they got worn out. I believe that those edges were consciously removed when the instruments were transformed.
In this picture I have drawn a flat front blade. Notice that in such blades, while I only have marked two, there would be a lot of waves reaching the ribs of the instrument in an undisturbed straight line from both feet of the bridge. That's why the flatter a blade is, the clearer is the sound it produces. So I think I understand why the front blades of Stainer's violas have a lower arching than his violins: to make his violins sound darker and his violas clearer.