Amazingly you have figured it out exact !! 10/10, you must know your stuff!!! Aah but there is a small error, the wiper shown from pin 6 should point to the right Pin 1, this is where the position would be relavent to the wiper position of the left set up. but still well done!!
as you can see from your own diagram, and the position shown by your wiper arrows is with the pedal in the up position, hence resistance between terminal 1 & 6would be at its lowest (with your wiper pointer (pin 6) switched to the right towards pin 1, and same again for the lower track, the resitance between 2 & 3 will be lowest,
So you really need to check what voltage you are getting at pin 6 and pin 3 which are the two wipers, and also see what voltages are at all other pins, with pedal in the up position and the pedal in the down position, all voltages measured against vehicle earth or ground reference. This should give you enough idea what to do or which pins to modify either by placing a series resitors or shunting voltages using a paralell resitor.
The trick was the two solid tracks which you said ran at the back on the top strip and the bottom strip, as they make the top strip and the bottom strip as a wiper point.
Just updated your diagram accept the wiper is now in the position it should be.
Pins 3 & 6 are the actual sensing pins, where the potential changes due to the pedal position, so I belive inserting a series resistor in pins 3 & 6 won't do the job as this will only effect the current and not the voltage, but I beleive that altering the resistors to the other pins of the potentiometer may alter the required response by adding or inserting a series resitor to any of the pins 1, 2,4 &5 but not the 3 & 6, as I strongly beleive the ecu senses the voltage rather than the current sense through this variable pedal control.
I would experiment with something like a 5K preset and alter to see what happens to accelerator response, wheather you get any ECU faults due to ecu sensing a tamper with values. and then if it works , fine tune the presets and wire it to a switch so that as you could choose which response you want as you stated.
