Trouble when using 4x10Gbit/s X710 PCIe ethernet card with optical port

Hi, we ran into some issues while using the 4x10Gbit/s X710PCIe ethernet card with optical port. We got a rate of 39.5G+ when using iperf2 between two PCs, but only got 36.5G+ between an Orin and a PC. We don’t know what causes such a difference. We did such tests as following:

1, Optical port PCIe card, between pc and orin, got 36.5G+;

2, Optical port PCIe card, between two PCs, got 39.5G+;

3, Another 4x10Gbit/s x710 PCIe card with electrical port, between pc and orin, got 38.5+G, which can also meet our requirements in terms of rate, but we want to use optical port if possible;

4, electrical port PCIe card, between two PCs, also got 39.5G+;

What factors could have led to this result? And how can we increase the rate when using our optical port PCIe card? We would appreciate if got any suggestion.