FlySky micro receivers ground level range test

This is unscientific receivers range test, made at the ground level. My transmitter (Flysky FS-i6) was placed on the roof of the car and I went for a walk with 4 receivers. Receivers that were used in this test: 8A Mini Receiver - Flysky FS-A8S - FS82 - FS-RX2A - FS-RX2A started to loose signal at the 60-80 meters, FS82 had solid signal link up to the 400meters. At the 500 meter mark all the receivers were out of rang