Cp is scaled by the reference values you define in the reference values panel. First, check if those values are correct for your simulation. Second, Cp is scaled by a characteristic velocity, which becomes uncertain in your simulation. What is a characteristic velocity of a free-falling accelerating object before it reaches its terminal velocity? As its velocity increases and so Cp will vary. I'd say you probably should be using the terminal velocity as characteristic velocity, but the problem with this is it is not knows apriory. So what you can do when presenting results is state what characteristic velocity you used to scale it.
Finally, Cp is used to define the pressure coefficient. Center of pressure is something else.
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