Calculating scale from cm/px to cm/cm for specific drone

Hi all, sorry if this is a stupid question regarding possibly simple math - but I am completely new to photogrammetry…
My use case is I have a CAD file which a ground surveyor created in Autocad of a plot of land that is ~800 square meters. The scale on the CAD file is 1:625 (cm/cm). I would like to use dronedepoly to create a mapping of the same area and then overlay it on the CAD file to see if there are discrepancies.
The problem is that when setting the mission it gives the scale as cm/px - centimeter to pixel, and when changing the altitude of the flight this scale obviously changes. How can I set an altitude in advance that it would give me the correct scale in cm/cm instead of cm/px. I’m guessing this has to do with the resolution of the camera (amongst other things). It would be a nice feature to be able to set which drone you have so based on auto settings it could tell you cm/cm instead of cm/px.
Any help would be greatly appreciated - I’m flying a DJI Mavic Pro and camera is set to highest resolution.


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