Is it possible to show a gradient between bars but only when above/below?

What I achieved using BetweenBarsData:

But I would like to create something like this:

Use the issue's two screenshots as the visual reference and first trace the bar-chart rendering and BetweenBarsData behavior in the repository. Confirm how the chart represents regions above and below the bars, then define completion as rendering the requested conditional gradient while preserving the existing behavior.

Written by the indexing model from the issue text.