My setting is
SF 6/7
CR 4/5
BW 250kHz
Freq 865 to 869
19byte payload
With crc n implicit header.
I get perfect comm up to 300m. Antenna is handtuned, reception via SA shows good output, including at the receive side.
When RSSI drop to about -70dBm, SNR starts to drop to negative region randomly, and start to loss packet.