frostWideMixEdge property
Wide-tail weight where the lens samples at the outline; with
frostWideMixCentre it gives w = mix(edge, centre, sampleDepth / halfMin), minus the size term of frostWideSizeRef, clamped to 0..1.
sampleDepth is the depth of the point the lens samples, so the band
(which mirrors the interior) gets the interior's weight.
Implementation
final double frostWideMixEdge;