PTP550 Throughput test via File Transfer

Recently we installed ptp550(400 meter distance, RSSI - 35dbm from Ap, -23dbm from SM, Modulation 8~9 from both end most of the time).

We tested with iPerf following instruction from cambium community ( Bandwidth test result was stable  400/400 mbps bi directional. One directional test (iperf) was 500/500~600(same as device GUI) . Now client want to test it with their networks. They want to test File server>client (3/4 laptop) to achieve same performance. For this how we setup our test environment for this?  We tried file transfer between 2 laptops on each side. We got nearly  40% of Iperf test.
If we can achieve at least 80% of iperf result via file transfer they will accept it.

Any suggestion??