IPERF and Orbi RBK53

I'm doing a few iPerf and I'm getting unexpected result.

 

When I run the iPerf from my router (Synology RT1900AC) / computer I have a normal result (980Mb/s).

 

When I run an iPerf from my computer (connected on my router) ----- my router connected to the Orbi on WAN1 and my computer connected to the Orbi with Ethernet I only get around 600Mb/s sometime even less (400...)

 

That's very unexpectred for a local / ethernet result isnt it?

 

Also I did other iPerf :

Main Orbi to the Satellite, my computer to ethernet via the sat , I get a very bad 300Mb/s (the satelite been 45Feets away in a straight open line).

 

When I connected to wifi instead, the link that MacOS report or even the Orbi app is 868Mb/s although the Iperf result is between 180 to 260Mb/s

 

How come my result is so bad? I have a 1Gbit/s internet connection which is a bit pointless at this stage.