Once a Notice to Owner has been sent out the full amount applies.
With reference to your other thread on this subject, the fact that an area is pedestrianised doesn't stop it from coming under the same legislation as a road. If, for example, you were to park on a grass verge (or paved area) where there were yellow lines on the road, you would still be subject to the restrictions imposed by those lines (even though you were parking outside of them). So the fact that you parked in a pedestrianised area doesn't mean that 'road' restrictions don't apply and, just as with parking on yellow lines, there is no obligation for a council to display a notice relating to penalties.