Have you read this? It might help.
https://boomerbenefits.com/tricare-a...are-advantage/
"Further more, when you have both, Medicare Advantage is primary and TFL will pick up the copays on your Medicare Advantage plan, leaving you with little out of pocket. Also, since TFL already includes drug coverage, you can enroll in an MA-only plan (without drug coverage), many of which have a $0 premium."