TEST Glass fiber antennas - Issues?

Issue: significant difference in reception between several antennas


Server: private/Chirpstack

Due to reception problems we have tested 4 RAK LORA 860-930 MHz glass fiber antennas:
NO. 1: 5.8 DBI
N° 2 and 4: 3 DBI
N° 3: 3 DBI (860-880 MHz old version)
Test tool: Adeunis field tester device
Distance 2 kms horizontal, at sight

Result: big difference in reception between the 4 antennas, see pictures.

Do you have an explanation for this problem?
Why is the 5.8 DBI antenna worse than the 3 DBI antennas?
Thank you for your clarification,