BLISK restricts policies to CNF: a single top-level AND over OR clauses, because the only MuSig2 KeyAgg happens at the top.
So an expression like A ∧ (B ∧ C) is compiled/normalized to A ∧ B ∧ C (three 1-literal clauses), i.e., just standard MuSig2 3-of-3, no additional security proof is required beyond ordinary MuSig2 for that part.