HR service delivery is sold on deflection, and the quoted numbers assume a knowledge base that is complete, current and reachable. Most are none of the three, which is why the deflection achieved after go-live so rarely resembles the business case.
This estimates your ceiling from what you actually have, and names the specific thing capping it. Deflection is bounded first by how much of your volume is genuinely repetitive — you cannot deflect a case that needs judgement, and no amount of virtual agent changes that.