Schedule 6 para. 2(4) of the RTA 1991:
https://www.legislation.gov.uk/ukpga/1991/40/schedule/6
Their website is wholly improper as is the NTO because individually and in combination they misinform an owner of their right to make representations which, as the Act makes clear, is not restricted to a single ground, neither do they fall into the website's arbitrary groups of PCN Improperly Issued etc.
It is wholly improper for the authority to restrict an owner to selecting one ground. So, IMO tick 'contravention did not..', ' penalty charge exceeded..' and 'other reasons'. Under the 'other..' ground put that it is contrary to the Act's requirements for the authority to attempt to restrict an owner to a single ground!
Now do you think they really know what they're doing or are they just doing it 'their' way because that's what they've always done!
This is my problem with local authorities, they don't want to spend money to do anything correctly but want everyone to pay through the nose for X, Y and Z.
Had they repainted those bays to promote them and actually make them usable for disabled drivers it would have been obvious and I'd have never parked there. They simply didn't want to spend the money so just put a sign up and started enforcement, effectively trapping people like myself who have parked there for years and get there early while it is still dark.
Perhaps their thought process was that people would nose dive in, in which case the sign would be right in front of you. They obviously didn't consider that people may dare to reverse, given it is way easier, especially for the first bay.