Last Post: July 7, 2010:
The RTS/CTS will be directed to the BSSID or the client - but that's not the most important thing.
What's important is who (meaning client or AP) HEARS it. Any device in the BSA who hears it must follow the rules - if it is following the rules.
By CCI, I assume you mean Interference, and not CCA - Clear Channel Assessment.
Different devices may perform CCA differently.
Protection is another issue. Search on "Protection Ripple" on this website - one of the latest CWNP book CD's has it too.
Do you have a spectrum or protocol analyser?
Remember ESSID is the same as SSID for Extended Service Sets (you won't find ESSID mentioned in the 802.11 spec.)