You did miss something. Your sim has different connections from the circuit shown in post #6, particularly around the op-amp to which the sensor (R6) is connected. That would account for why you don't get the expected results.
I've done the sim in LTSpice, based on the circuit in post #6, using the circuit below. Note my zener D6 in the power supply is inverted compared to yours (correcting what I think is an error in the post #6 circuit). Note also the simulated power supply gives V+ = 13V, V- = -5V and Vref = +5V rather than the voltages you have used. My sim and the results are below. The curves are for 4 different values of the sensor resistance (50-200 ohms). I can post the .asc file if anyone asks.