An IRA is a trust and the legal (as opposed to beneficial) owner is the trustee on behalf of the trust. The account is in the name of the trustee for the trust. You will see it on official account documents which will show the tax number of the trustee. You are just the beneficiary. You are not the legal owner of the account (despite sloppy wording by some brokers). So coverage is indeed separate.
So.... the consensus is that you can have both a $250k margin account AND a $250k IRA account with the same retail broker & BOTH will be fully insured by the SIPC?