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I don't think we can make a rule of thumb on this point. Long rad hoses do add a tiny bit of friction, or considerable weight if sized for truly minimal resistance. A rad in the nose is more likely to be able to get by with minimal fan use, but it can disrupt air flow over the rest of the shape. OTOH, scoops for natural air flow through the rear are another hazard to the low cd. Then you have to consider the often lower efficiency of air-cooled motors, which develop hot spots. Electric vs mechanical fan drive is affected by possibilities of variable fans and drives. Also, if your shape is streamlined and your weight is low, it pays to have batteries and or motors up front for natural stability without needing fins for balance in crosswinds. But then, you might want the sailing benefit of the fins if you have overturning resistance to spare. . . .
We can change anything, but we can never change just one thing.
Designer's Lament
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