The throughput is measure with what you mean only useful data. Nobody will calculate the wireless overhead.

TL-WA7210N is able to cover 2km so if you use the device correctly you shouldn't get such short coverage distance. So how did you judge how long the device covers? Besides, TL-WA7210N uses build-in...

SNR is the ratio of Signal Strength to Noise Strength. At first there are only two devices communicating, wireless environment is clean. After the second client joins the network, they will compete...

The main question is coverage area so if you are sure in the deployed triangle other two CPE510s are under coverage 3 units are enough.

Did you install external antenna on the access point? If yes please tell me the number. I suspect that's because of the improper deployment which leads to instable connection. Position and angel are...

No extra operation needed to configure for router 2. Try to wired connect another PC to router 2 and see if any improvement. Once nothing change, Ping the WAN port of Router 2 then TL-WA5210G then...