Thanks. No, the part that has lightened was that part that wasn't covered. KBT first then KRST. It became lighter. The part that was covered didn't receive KBT. When KRST was applied to this portion, it did extend the black. Brown toner itself made the density at the dark part lower, so it became lighter. Changes in density at highlight area weren't that obvious. (color change was)
It would have been easier if I could post the image but I am not able to scan it to really show what I want to show, so I didn't. Thank you for your idea though.