Hi @hasheduhash,
LoRa radio is low-powered, so it shows its best in rather open areas with a line of sight between the base and rover. In great environmental conditions, the LoRa range can be even more than 8 km. You can check one test with a long LoRa range in this forum thread.
When the line of sight is obstructed, the LoRa baseline can significantly decrease. In such cases, you can work with the Emlid NTRIP Caster or try a pair of external radios, as Gabriel suggested. Overall, Reach RS2 can work on up to 60 km baselines in RTK.