matching op capacitanances with impedance plot

Hello , I am trying to validate my output impedance plot with the OP parameters of the mosfets connected to the output.

the Cds and Cgd capacitances were shown in the zoomed plot bellow.

i have made an Idc source with AC=1V only. and plotted the imaginary part of the output node shown bellow wher Z_ac=V_ac/I_ac

imag(vfreq('ac "/net18"))  shown bellow.

However if we look at the imaginary part of the impedance and we see capacitance profile from the output Z_c=1/jwc then the plot should descend,instead it stays constant and starts to rise as if it was and inductor after 10M.

I tried to extract the capacitance from two points i notated on the plot bellow and both of them doesnt match the 10fF capacitance we should have.

Where did i go wrong matching the capacitance from the plot with the capacitane from the OP?

Thanks.

point 1:

42.1=1/(2*pi*10000*x)

3.7804×10^-7

point 2:

38.21*10^3=1/(2*pi*10000000*x)

4.16527×10^-13