According to CCC's website the aim of the Ricoh Arena Residents' Parking Scheme is:
"...to make sure there are no parking problems on major event days, where more than 10,000 people are expected at the Arena."
The implication of the above is that the scheme should not be being operated when less than 10,000 people are expected. Of course, there is no information on the web about how it is determined whether more than 10,000 people are expected (does an individual at the council just guess, does the council ask ACL how many people are expected, does it ask the club).
All of the legal particulars about the scheme should be shown in the Traffic Regulation Order for it (a legal document drafted by CCC). The Traffic Regulation Order for the scheme doesn't seem to be available on-line, if someone was particularly interested they could make a FOI request to get a copy of the Traffic Regulation Order. Personally, I suspect it might make interesting reading as I have a feeling that the scheme is being operated beyond the parameters set.
Regards enforcement of parking restrictions at Tesco, something that hasn't been mentioned yet is the possibility of a planning restriction. It might be that parking in the shopping centre's car park is subject to some timelimit as a result of planning constraint (the intention of which was to force motorists to use the Arena's car park that was owned by...).