LTspice: Building and Simulating the MMBZ5236BLT1G Zener Diode Model

While simulating ON Semiconductor’s MMBZ5236BLT1 in LTspice, the datasheet specifies a dynamic impedance of 500 Ω at 0.25 mA, but the actual simulation plot (shown below) exhibits a significantly different slope in the low-current region. The SPICE model I’m using is as follows: