I’ve done 2 range tests so far; 11km and 13km. Both were clear line of sight, and both gave about 80% signal strength on the display.
Hardware T-Beam v1.1 865, standard antenna
Firmware v0.7.9 and v0.7.10
Channel setting: Very long range
I think 20km would not be a problem, with the standard setup, I will try in the next week or so.