Blend Layer Anchor
blend-anchor
Sets which point of the blend layer image is placed by blend-x and blend-y. The default is the top-left corner.
Valid values are alignment words such as top,left or middle,center, or an x,y pair of fractions of the image itself.
Use blend-anchor[N] to target a specific blend layer, where N is 0–3. Layer 0 is either the bare blend-anchor or blend-anchor[0]; if both are supplied, the bare name wins.