2.5gbps uplink on EAP670 speed not as expected
I have two EAP670 currently connecting to my TL-SG3210XHP-M2 using the 2.5 poe+ port. These two EAP works find on both 2.4ghz and 5ghz band and can give 600-800 gbps on my phone if I'm in the same room which is good. However, I'm expecting multiple device connecting to EAP670 can utilize its 2.5gbps uplink port that connect to my 2.5gbps switch.
I experimented with 2 mobile devices that connected to EAP670 and run iperf3 client that connect to two different servers that also are on TL-SG3210XHP-M2. If I run 1 mobile device I get 600-800mbps and if I run 2 mobile devices I get a total of 600-800mbps. I made sure the 2.5gbps port on my TL-SG3210XHP-M2 is fine by testing on my PC so I'm wondering if EAP670 is just not capable to utilize its 2.5gbps port due to hardware limitation or maybe there's some setting I need to enable. Thanks.