Unstable Downlink Message in Class C OTAA

Hi, I used the Dragino L308 as gateway, Heltec LoRa 32 v2 with a light as a node and the ChirpStack network, application server and bridge for my light control application. Besides , I used classC OTAA mode.
In the range of 1.2 km, i kept seeing uplinks in my data log with no problem. However, for the downlinks, only at few locations with line of sight to the gateway, it can receive the downlinks to turn the light on and off. For other location, I can not control the light.
Does anyone know the reason? What kind of setting I need to do with my node to get a stable downlink? For example, datarate, dutycycle…
I would be really grateful if I can get an answer. Thanks in advance.


For Class C, I think turn on “CONFITM” button when downlink may help increasing the stability.