Headlines miss the nuance: Coherent's CEO says they alone run six-inch InP — >4x die per wafer at under half the three-inch cost, across three qualified sites. Yet three-inch isn't lagging. InP is brittle and thermally sensitive; larger diameter brings stress, warp, and defect challenges together. Industry commentary confirms bigger wafers only pay once yields are controlled. Six-inch mastery is the unusual feat; three-inch stays the sensible baseline. In precision work, wafer size matters less than yield-curve discipline. Whatever the substrate, it still needs aligning. That's my domain.