I would be very surprised if the PCiii does not have a smoothing factor that determines the various offset injector pulse width percentage points on either side of both axis - RPM and TPS.
i.e. if you are using 500 RPM steps, and the default TPS steps, then if you entered a value of (+) 10% at 5000RPM and 40% TPS, it would MOST LIKELY gradually reduce the 10% offset to 0% from 5000RPM down to 4500RPM (the next lowest RPM point), and similarly reduce the offset from 10% down to 0% at 5500RPM (the next higher RPM point), but with say 5% at 5250RPM and 5% at 4750 RPM.
Similarly, I would expect the PCiii does the same for the TPS grid, in this case, it would reduce the 10% offset at 40%TPS down to 0% at 20%TPS, with maybe 5% at 30% TPS, and again, it would reduce the 10% offset from 40%TPS down to 5% at the next higher TPS point of 60%, with maybe 5% offset at 50%TPS.
This is all conjecture on my part, and would need to be checked with a wideband O2 sensor or gas analyzer, but it makes no sense for the PCiii to affect only the specific RPM and TPS intersect points of the matrix ( 10% richer at 5000RPM, but 0% richer at 5001RPM or 4999RPM!)