1095a ACA question

Here is the situation of someone whose taxes I’m assisting with:

- parents used ACA (marketplace plan) for the full year

- 22 year old child that is NOT a dependent for the 2019 year was on the same marketplace policy where an advance credit was made

- 22 year old started a job in August where the employer offers affordable insurance but did not take the employers coverage.

 

what will be a beneficial allocation between the parents and the non dependent child? Would it be more beneficial to allocate 80% of the policy to parents and 20% to child or 95% to 5%. We want to avoid having the child pay back the premium as much as possible. Any thoughts are so welcome because we are spinning our wheels.