As I understand it, the salary cap limit for NL1 is, I believe, ?150,000 or 50% of your income up to a limit of ?400,000. However, if it can be shown that your income is in excess of ?800,000 per annum, that salary cap level can be raised again. So, if Cas have an income of, say, ?1,000,000 they could go up to 52.5% of that before they would break the rules and that would give them a salary cap of around ?525,000.
Obviously, it is in every clubs interests to have as much income as possible to get a benefit on the field.