Depends on the wheel.
Rim shame can have a very large effect on drag, further, the yaw angle (which will change with wind speed, direction and your speed into it), the speed you are riding at, the tyre mated to the rim etc.
Also the effect of the wheel on overall drag will vary depending not only whether it is placed on the front or rear of the bike, but also on the frame you fit it to. Some wheels produce less drag than others on certain frames, yet the result may be the opposite on a different frame.
IMO, if this is just an exercise in academics and you are not deciding what to buy, I would advise you look at tunnel data published by HED and Zipp (easy to find) or similar independent studies, they exist, look harder.
If it is for the purpose of informing a purchase decision, I would just say, unless you are at the sharp end of TT results, then buy the one you can afford/looks best/matches your bike! If talking rear wheels, always buy the disc wheel, they go rumble rumble!
BTW, I have a set of FFWD wheels.