Unfortunately, radio frequency is affected by things such as obstructions, terrain, weather, material, etc., which all degrade radio signal.
Retevis shows the maximum range that can be reached by a model in ideal conditions. Ideal conditions include no obstructions between you and the other person, a fully charged radio set to high power, and communication over a flat surface such as water or mountain top to mountain top.
High power have long communicate range. chlik it to knowledge the retevis long range radio