The 4980H(b) penalty applies when you offer coverage (like CHOICE), but the offer is considered unaffordable for a specific employee who then claims a premium tax credit. The penalty is $4,460 per year ($371.67/month) for each affected full-time employee.
The total 4980H(b) penalty is capped at what your 4980H(a) penalty would have been. This penalty is assessed per employee who receives an unaffordable offer and takes a subsidy, not across your entire workforce.