Auto TX power control on FortiAP is an RF-optimization feature:

FortiGate (as wireless controller) continuously evaluatesRSSI of associated clientson each FortiAP radio.

The algorithm focuses on theweakest client(the one with the worst signal) and adjusts the AP’s transmit power so that this client’s signal level stays within a configured / target range.

This helps balance coverage and limit co-channel interference: APs don’t transmit at maximum power when clients are close, but will increase power when the weakest client signal drops too low.

Therefore the correct behavior description is:

✔C– AP power is adjusted based on the weakest associated client’s signal.

Why the others are wrong:

AandBtalk about matching nearby APs’ power or forcing everything to –70 dBm, which is not how FortiAP auto TX works.

Dincorrectly states the AP “evaluates its own transmission from the client perspective”; the AP can only infer client-side conditions from theclient’s RSSI at the AP, not the inverse.