You have an OBD-2 ECU which can detect advanced timing and compensate. So if you've been driving around with the car like that for a while, your ECU has probably already figured out what's going on.

However I believe the reprogrammed ECU is probably the culprit. The stock ECU is perfectly capable of reading the amount of air going into the motor, so if you have an intake or something it is aware of the change and makes the necessary adjustments to still maintain the set factory a/f ratio.

Except I just realized...your car is OBD-2. So I don't think anything has been done to the ECU since nobody sells OBD-2 chips.

Either that, or your car is just slow.