KC=timing advance map value * IAM/16
KC will change depending on how much advance you run. It is also based on a few feedback correction maps which will adjust timing based on knock.
Negative KC in theory would be a result of pulled timing and you could try and tune all negative KC out, but it will be difficult. Timing is sometimes pulled off throttle and when knock is detected on tip in.
In addition, some logs I have seen have shown a drop in KC with no drop in advance or IAM. KC didn't go negative but dropped from 9 to 3.5 at high RPM. I am still trying to figure out what happened there.
Look here for more info.