My best advice for this is to keep in mind that when it comes to 802.11 communication, there isn't a difference between an AP and a STA.
Always think of 802.11 communication in terms of "Wi-Fi communication on a certain channel in a given area". If that given area (from the perspective of the 802.11 device) happens to have two APs then your concern should be the amount of traffic that each device is transmitting (and receiving for that matter).
The term "co-channel interference" is really a bad term, although I am guilty of using it. Two 802.11 devices on the same channel don't interfere with each other, at least not from an RF perspective. They can interrupt each other (collision) but it is not technically interference. If it were to be called that then a STA and AP on the same channel could be considered "co-channel interference".
Adjacent channel interference is truly RF interference as the devices cannot understand the protocol of each other but they will cause data corruption.
A person could say from your situation that the AP's TX power could be lowered since you have quite an overlap. However, that isn't realistic to lower power for just one area of overlap. In a real environment you will have varying overlaps because of the varying RF propagation that occurs with almost every enterprise installation.
Sorry for the long winded answer. Let me know if I can clarify anything further.