source to drain capacitance of pass transistor under OFF condition

In my circuit a pmos or an NMOS transistor is under off condition. Voltages at both the ends (source and drain) of the transistor are equal. Under this condition, is capacitive coupling exist between source and drain ? If yes how to derive it? (i.e. coupling capacitor between drain to source, Cds).

Perhaps this relates to your other thread.

Cds always exists. At advanced process nodes you
may see as much Cds from the interconnect as from
the actual intradevice junction and overlap capacitances.
Any derivation will likely be far off unless you know a
lot of detail about junction depths, geometries, side
diffusion and oversizes even if you did have a layout
to look at. Characterize, rather than calculate. Unless
you are good at TCAD and have plenty of time to kill.
Or believe what the models tell you, these hopefully
being data based and reviewed for reasonableness.

Thanks. You are right. My this questions is related to other thread as you have pointed out. I have a circuit in which a nominally OFF PMOS pass transistor exists in feedback path. Input of this pass transistor is connected to a high impedance node and output of pass transistor is connected to an active node. The voltages at both the ends of pass transistor are same (i.e. 3.3V). I am simulating an exponential current pulse of rise time (50ps) and fall time (250ps) at the input (which is at high impedance) and observing that there is a current flow from input to output of pass transistors as voltage at the output node of pass transistor reduces to zero.
My questions are:
1. whether the source and drain terminals of OFF pass transistor act as short, initially, due to Cds exists between source and drain terminal and Cds offers low reactance initially to the current pulse and cuts off the series path as it charges due to decrease in voltage at the other end?
2. Is Cds dominate under OFF condition of pass transistor and offers low reactance to rise time of a current pulse?

thanks and regards