Being mentioned and being recommended first are different things. Top-Ranked % captures the second: of the AI answers that mention your brand, the share that put you at #1. The single top pick, not just somewhere in the list.
It's the sharpest read of preference. Two brands can have identical Share of Voice while one is consistently the lead recommendation and the other is perennially "also available." For high-intent buyer questions, the top slot is where the trust, and the click. Goes.
It pairs with Average Rank: Top-Ranked % is the headline "how often am I first," while average rank shows where you land the rest of the time. A brand can have a modest Top-Ranked % but a strong average rank (usually 2nd-3rd), or the reverse. The two together describe your real competitive position.