There could be many factors including which region you are in.
In the UK ch165 isn’t allocated for WiFi but for indoor/outdoor Short Range Devices, such as video links for home security, remote security sensors, etc, even analog FPV transmitters. These devices could be transmitting at 100% duty cycle / constant carrier, over large bandwidths. The channel guide in the Anafi App will not show these as it only shows signals from genuine WiFi emitters. So if you are flying in an urban environment with a lot of this activity the chances of interference will be high and your range much reduced.
Terrestrially speaking 5.8GHz has a reduced range capability when compared to that of 2.4GHz so if you’re flying in an area with low activity in this allocation it might be worth manually changing the channel to one between 1 and 11 on 2.4GHz. The received video might be lower quality as the bandwidth will be smaller but the range will increase. Also the further you fly from the point of take off the pointing accuracy of your controller becomes much more important. The Anafi controller does have a relatively wide beam width but still very directional.
My personal experience is attaining a range of just over 2km on 5.8GHz but this was on flat farmland well away from any other radio signals. This max distance wasn’t due to loss of signal but due to some grumpy members of my model flying club bumping their gums because I was doing something that appeared to be witchcraft to them.
Regards
Nidge.