Is the quoted range of an RF module based on two identical modules?
There are two things to consider about radio transmissions. One is the power output and how far that can be expected to be reasonably detected and the 2nd is how much bandwidth you are using because this limits the signal that is needed by the receiver. 

Starting with the receiver, at a given data rate it can be expected, at ambient temperatures to successfully receive. -154 dBm + 10log (data rate). So, at 1000 bps the anticipated signal strength needed will be -124 dBm. At 1Mbps this increases to -94dBm.

Given perfect conditions a transmission will attenuate at 32.5dB + 20log(MHz) + 20log(kilometres), so at 1GHz and 10km, the output power from the transmit antenna is reduced by 32.5 + 60 + 20 decibels = 112.5 dB reduction and if you were transmitting 1000 bps at 1 watt, you'd probably be ok with minor obstructions and reasonable line of sight.

You should be able to estimate what the real distance of your actual radio modules are now and report back how they stack up against the marketing claims.