coverpoints must be integral expressions. You have a few options
- Create an array of covergroups and have each covergroup sample a different element of your unpacked array.
- cast your unpacked array into an integral variable and cover that. (not a likely option here).
- Create a function or some additional code that reduces the set of data down to a manageable integral coverpoint.
You will have to explain a little more about what you are looking to get coverage on this large amount of data.