Pitch Trim - Stab/Elevator vs. All Flying Tail with Trim Tab
Microburst,
Stepping back to examine un-augmented airplanes for a moment, there is a difference between an arrangement with a stabilizer and elevator (most common on large commercial transports) and an all flying horizontal tail with a pitch trim tab.
With a stabilizer / elevator the full horizontal tail (the stabilizer) moves slowly in response to pitch trim inputs. The pilot's primary pitch control input (column or stick) commands the displacement of the fast moving trailing edge surfaces attached to the stabilizer (left and right elevator). The column/stick input defines the position of the elevator relative to the stabilizer. With this arrangement, pitch trim is achieved by trading stabilizer for elevator. As the stabilizer is moved in the direction of the elevator, less elevator is required. The pilot relaxes the column/stick. Pitch trim is complete when the stabilizer has moved to the position where it generates the desired pitching moment with the elevator at its position corresponding to column/stick centered with no force.
With some (typically smaller) airplanes that do not have separate elevator and stabilizer surfaces the pilot's column/stick controls motion of the full horizontal tail. This arrangement usually includes a tab on the horizontal tail that is used for pitch trim. With this arrangement, the pilot relieves steady controller forces by adjusting the trim tab. The column/stick is not moved during the trim process. The tab applies aerodynamic force to the horizontal tail thus relieving the pilot's need to carry force. I believe it is this arrangement that you are describing where pilot controller will be at a variety of positions when in trim depending on how much pitching moment is needed from the tail to balance other sources of pitching moment.
With the stab/elevator arrangement pitch trim always occurs with the elevator in the same position. What varies is stabilizer position. As a result, pitch trim always occurs with the column/stick in the same, centered position on the flight deck. In this way, pitch trim on a B777 is very similar to pitch trim on a B737. On the B777 there is no mechanical trim wheel running back and forth on the flight deck when stabilizer motion is commanded, by the coordination between column and pitch trim switch inputs is nearly identical. The biggest difference is that on a B777 pitch trim is only required when steady speed has changed. On a B737 pitch trim is required for other changes affecting pitching moment balance such as flaps, speedbrakes, gear, and thrust in addition to speed.
You are correct to state that implementation of C*U is more complicated than C* alone. Boeing made a design philosophy decision during development of the B777 to provide convensional speed stability and thus speed awareness through through column forces throughout the flight envelope. Pitch trim is required for speed changes and the airplane tends to maintain trim speed. Pilot workload is slightly higher than with C* alone, but it was felt that keeping the pilot more in the loop was worth the effort.