Last I knew, technically, the insurance generally* only covers a person up to the amount charged to the card, but I've also seen people file successful claims after, e.g., charging only ~$10 of taxes to the Prestige on an award ticket.
Travel insurance has been used and abused by the "travel hacker" crowd in recent years, and almost every issuer has started to cracked down in one way or another. If you want the insurance, I wouldn't get too cute when it comes to charging 90% to one card and then the last few dollars to the Prestige.
(* Depends on the issuer.)