From Figure 4:

Diagram Output Power vs. LADJ Resistance:
When LADJ Resistance = 0 then the output power is 9 dBm (7.943mW).

In theory you can get 10mW but then when you read:

The LR Series transmitter is designed to generate 1mW of output power into a
50-ohm single-ended antenna while suppressing harmonics and spurious emissions
to within legal limits.

* * *

In unidirectional links, a good designed transmission protocol will make the difference.
Use redundant data for the purpose of error correction.