Although it is affecting the whole range, it acts as a percentage of the idle fuelling, so has less and less effect the more you move away from idle.
Mot rules are getting tighter, no adjustment can be made once mot test has started, but a quiet word I'm sure most would adjust prior to starting the test proper.
The thing about adjusting for mot and then back to where it should be is a excuse for either a shit ecu or mapping job on the chip, or both, ie complete bollocks, should not be needed.
If I can get through on greys, with 180,000+ miles on bottom end no one has an excuse, my co is as it runs normally, ie NO adjustement whatsoever from everyday, at 0.97% CO, but then it's mapped correctly and runs like a dream.
tabetha