The UHF antenna is tuned for 410-470 MHz which is a completely different frequency band to LORA 900 Mhz and would not work properly.
LORA is low power at only 0.1W and very line of sight. If you are amongst trees, buildings or over hills the signal will get blocked and reduce range. Thats just the basic physics. I get a few hundred meters in the bush here with LORA and I’m happy with that given what it is.
A UHF radio will work bit better in difficult conditions at the lower frequency, and push out more power with some up to a max of 35W but they require a licence. Horses for courses.
EMLID don’t (yet?) have repeater capability but it is possible to get an aftermarket longer range LORA antenna kit but I haven’t tried one so can’t vouch for it.
There are some tips here that include tweaking the frequency and lowering the air data rate that may help extend the range: How to configure LoRa for RTK on Reach RS2+ - Support tips - Emlid Community Forum
And it’s even possible your RS2/3’s are simply configured differently.
Otherwise you could use Base Shift in Flow to get the base closer and/or higher up overlooking where you are working.