Enrolment rule at option level to restrict opt out

Hi,

We have a life assurance benefit plan which defaults eligible employees into core cover and they are also able to additional cover. For the core cover, they are defaulted in based on eligibility and they are not able to opt out core cover. For example, for one population, they should be defaulted in 9 x Salary Core Cover and able to select 1 to 5 times Salary as additional cover.

My question is what enrolment rule i should use at the option level (9 x Salary Cover Cover) to enable people defaulted in this option and not able to opt out?

And this is how i set up at the plan level for enrolment: