Communication distance is determined by four factors:
Output power, recieve sensitivity, Antenna systems and the environment.
Visit this application note for Maximizing Range.
(Also please see Distance and Obstacles document with Fresnel Zone: https://www.digi.com/resources/documentation/Digidocs/90001942-13/#concepts/c_distance_and_obstacles.htm)
Actual performance varies in each environment. Digi strongly recommends that no radio decision be made without evaluating all radio modem candidates in the actual environment of the application.