Thanks! I increased the composition size, shifted the "excluded" layer over, then made it the uppermost layer, and that accomplished what I was after.

Hey all, I'm using the Advanced Output mapping for the first time, and I'm butting my head against something. I have some slices assigned to Layer 1 only, and I have other slices assigned to Composition. I would prefer that the Layer 1 content NOT also appear in the composition output. I'm imagining...