Hello.
Could you please tell us about parameter frame size (2,5 or 5 ms)?
Does AP create modulation to all clients or its shared between them?
What level of RSSI Downlink dbm is good for SM and which level doesnt recommended for use?
Frame size (no relation to ethernet frames) is the duration of the full cycle of send then receive, then back to send. (plus overhead for SMs requesting upload slots, etc) So with the 2.5ms frame size you will test lower latency across the link. However, when set to 2.5ms you'll have twice as much capacity spent on the frame structure itself (like uplink scheduling, etc), so less capacity available for client data. So oversimplifying, 2.5 is better for low latency, 5 is better for sector capacity.
If I read your second question correctly, then Yes the AP tries to run the highest modulation it can to each client, based on it's connection to that client - only sector-wide data (like ARP and other broadcast data) will be on the same modulation for all clients, either MCS0 or MCS1 depending on your selection for "Management traffic Rate" just below the frame size setting.
Downlink dBm is best IMHO in the -50s, I would be careful if the signal is able to exceed that (into -40s) but honestly I don't pay as much attention to the signal level itself, since interference sources are so very common across 5GHz and 2.4GHz bands - a more useful (IMHO) measure is the SNR, which I prefer to be mid-20s or better.
j