Given your code, the iff() syntax is redundant.
What’s the type of HSEL?
Depending on the type, then it is likely that, for instance (HSEL == 4), might not evaluate true or that the bin sample value is never seen.
It would help if you could share the code for your covergroup. Things that would be useful to know:
- How are you sampling the covergroup?
- How do you decide when to sample the covergroup?
- What are the types involved?
- Which conditions apply for the sampling of each of your bins to be valid?
Have you checked what values are being sampled by your covergroup? Maybe you’re getting the right answer - i.e. that HSEL is always 1