Steven,
Now I am really confused. Please forgive me if I misinterpreted what you wrote.
A portion of the eye of the dumbbell may project over to the other side of the hook shank on which it is tied, BUT that does not mean the center of mass or center of gravity of that dumbbell eye lies on the other side of the hook shank.
My thought is that whether the added weight is lead wire, or dumbbell eyes, the placement affects the center of gravity/mass of the fly. Dumbbell eyes move the center of gravity forward because they are generally placed forward on the hook behind the hook eye. That was what I was trying to do so that my fly would jig up and down, However, I had so much lead further back on the shank of the hook, the eye could not move the center of mass forward enough for the fly to jig up and down.
Bear with me for the following explanation of how I think dumbbell eyes affect the center of mass of the fly.
The center of mass/gravity of the dumbbell eye itself should be in the midpoint of the central shaft of the eye. Whether the eye is tied above the shank of the hook or below, does shift the center mass of the eye 1/2 diameter of the dumbbell eye shaft (and not the diameter of the eye) above or below the hook shank. Therefore the difference in these two locations is the diameter of the dumbbell shaft plus the dimeter of the hook shank.
This does shift the the center of mass/gravity of the fly a bit up or down but I think how the point rides also depends on how the hook is shaped and how the rest of the fly is weighted. The eye itself (because the center of mass is at the center of the shaft), even when tied above the hook shank may not be enough to flip the fly upside down so that it rides hook point up reliably.
Regards,
Silver
"Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy