Interventionist supply policy buys things: roads, training places, research grants. Market-based supply policy buys nothing and changes the rules instead, so firms and workers choose to invest, cut costs and compete harder. Raise the policy intensity and watch each stage of the chain light up before LRAS₁ moves; then switch the mechanism at the same intensity and see which stages change.
Indices are illustrative: they show the direction and order of effects, not measured sizes.
Market-based supply policies change incentives rather than buying capacity: the chain runs through investment or unit costs to productivity and only then to LRAS.