Hey, I was there! I flew the Hunter 1, which had a 4.2:1 power assisted elevator, and an electric moveable horizontal stabilizer [to pin things down accurately]. I also flew the Hunter 4, with a fully powered elevator, I think [don't have the piklots notes handy] and later marks with the high speed electric "follow-up" horizontal stabilizer, which I shall now call the "tail" for simplicity.
The later follow-up tail effectively gave the Hunter an all-moving tail, as the later Sabres had, and as the Hunter should have had from the begining. Until that fit its longitudinal control at high Mach was rubbish.
But I digress. Having talked about this, and with the benefit of all your advice, I still thuink I have the right answer. In a fully powered elevator/electric tail trim system stick force must be measured from elevator deflection, relative to the tail. So, if you are out of trim you are holding on some elevator. As you move the tail to trim out the stick force the tail gradually takes over the trim task and the elevator gradually gives up and reverts to neutral - mechanical neutral, in line with the tail. So, elevator neutral, no stick force. Tail takes over trim, attitude held constant.
In a power assisted system you still get stick force from the aerodynamic load on the elevator - only a piece, depending on the degree of power assist. Now, as you move from out of trim to in trim the electric tail is taking over, and the elevator giving up, but you reach zero stick force when the aerodynamic load on the elevator reaches zero - not when it is at the mechanical neutral. This will happen when the elevator is in line with the resultant airflow off the back of the tail. This airflow will be a downwash/upwash if the tail is at a high alpha, and will be zero when the tail is at zero lift alpha. Since the tail position will depend on what trim output is required it will vary with configuration and speed.
Many of us, and I digress again, suffered from a. the Hunter's lack of longitudinal control authority at high M, and 2. the nose down change of trim when combat flap was extended. The pitching in the resultant dive made it almost impossible to reach the flap lever and knock it up. Some of us recovered at low altitude, some did not.
Dick W