Stop dependents from being dropped for Marriage or Birth Life events

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How to prevent an employee from dropping spouse during a Birth life event? 

I used "can add dependents" on designation requirements (plan type level) for Birth LE. If an employee is currently enrolled in EE + 2 and spouse is unchecked, system throws and error. However, system is not preventing the employee to enroll in EE + 1 (with new baby as dependent) or for that matter EE Only.

I tried using "Current Enrollment Prevents change" at various levels - Plan, option etc, but, without any success.

Any ideas are greatly appreciated!! Since this is a common requirement, I hope there is a way to do it via configuration.