Hi Arjen,
This depends very much on where the gateway (-antenna) and node are located. Although line of sIght (LoS) is not required for LoRa it does help a lot. My 1ch gateway also using 8,6 cm antenna is placed inside in the attic (about 6 meters above ground level) in a "city area", also range isn't that good but I do get up to 2 km when also the node is high (like on a bridge). I now also have an iMST iC800A gateway at the same location with a better antenna. This performs "somewhat" better but not dramatically. I did not get a greater maximum range, but do get little further in some area's and reception is more reliable in close range (I have put my nodes on 1 channel for comparing this). This limited range is not a limitation of the iMST board, I know it can perform much better with a proper antenna on a good location,
I also see there is some "directional preference" for some area's (this probably has to do with buildings nearby). My RFM95 based node with wire antenna gets up to 17 km range when talking to a Kerlink gateway (in "almost" LoS conditions).
I plan to get an antenna for the gateway up outside in the next weeks and hope to get some better range.