Interesting that you tell the antenna needs to be high up.
I read other oppinions on a local forum, but there it is also unclear what the best position is.
The multiradar CD our law enformcent officers use (over 250 were bought last year) send with very low wattage en i think circular polirasation.
So detection distances vary from 150-200 meter with persons with the antenna behind the plastic of the front part of the car. One that is installed with free sight out gets 400 meter sometimes.