Series resistance will give you linear changes.
Rtotal = R1 + R2
Parallel resistance will give you curves and the total will be less than the smallest resistance (pot adjustment) and relative to it.
(1/Rtotal) = (1/R1) + (1/R2)
A microcontroller can use a lookup table to correct non-linearity of the sensor. There's room in a Teensy 2.0 to adjust _every_ step of all 12 10-bit analog inputs and still have room for useful code.
The most accurate stick I ever had used optical encoding. That wasn't analog at all. When the new hardware came out something changed and it wouldn't work so I sent it off to Rookie from the old Delphi FSF.
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