Temperature sensor siting: The sensor should be mounted 5 feet +/- 1 foot above the ground. The ground over which the shelter [radiation] is located should be typical of the surrounding area. A level, open clearing is desirable so the thermometers are freely ventilated by air flow. Do not install the sensor on a steep slope or in a sheltered hollow unless it is typical of the area or unless data from that type of site are desired. When possible, the shelter should be no closer than four times the height of any obstruction (tree, fence, building, etc.). The sensor should be at least 100 feet from any paved or concrete surface.
With an all in one, you cannot mount just by the temperature recommendation. You must consider the anemometer, and that is what Kevin did by putting his 5 in 1 on the roof. Acurite says at least 5 feet or more, based on my experience, I would say at least 10 feet, and 20 would be better, but over land.