Problem with communication range of 7243 and 5205

We have RAK5205 which is communicate with RAK7243 on the US channels (chirpstack). Our test made in flat field (outdoor).
In short range the communication is fine but when the RAK5205 in distance of 400m the connection lost.
For the sensor we use its original (short) antenna and for the gateway we use this -


Have you ever tried this antenna???

No we have not. The 5205 is actually your tracker - 7205 enclosure with a built in antenna. In any case 400m in a completely flat and open area with line of sight between the sensor and the GW seems too short. Do you have any range data from testing 7205? Are there any parameters we can change in either GW or tracker to improve the range?
Using the antenna you suggested is not practical as the whole point in 7205 is its enclosure

hi yairsharf:
Do you enable the ADR function when you testing? Or you just test with SF7 datarate?