Brief Description: Adjusting the forward elevator stop block
It was clear why my elevators would only travel 6 degrees forward. In Image 1 you see the elevator stop block protruding into the forward portion of the rear deck's elevator horn hole. It's supposed to be trimmed to the same shape as the hole.
I corner-drilled, then removed the excess plate, sticking to the edges of the elevator horn hole. Once filed down, I reinstalled the elevator and rechecked the elevator's travel--23 degrees, right in the heart of the envelope. Moving on...