I was looking at my 10M the other day, trying to figure out why it was so much more ergonomic in the right hand than either my Buescher tenor, or my SA 80 alto. The answer was the ring finger key is different and closer to the middle finger key, due to the design of the forked mechanism, and for me way more comfortable. On the other two horns my ring finger seems to always be half way on instead of right on like the 10M. Seems to me the problem with the other two horns could be remedied by making the 'stem' coming from the ring finger that the pearl sits on a bit longer, so it is in the same position as the forked mechanism.
Sorry for the inaccurate terminology but I don't fix them, I just play them. If someone out there is familar with my problem, and has come up with a cure, I'd love to know.