Guardant & Signatera cancer tests covered by Tricare

Has anyone had success getting the Signatera cancer test covered by Tricare? My wife is post triple negative breast cancer, 18 months since diagnosis, and has had several Guardant tests completed and paid for by Tricare to look for cancer DNA in her blood. The Signatera was done once and is a better test in her opinion because it specifically looks for her tumor DNA. However Tricare has denied it as they say it is not a covered test. Not sure how the first was covered unless the cancer center just ate the cost.