The bidirectional-diffusion controller sets the ancestor depth $d_\uparrow$ and descendant depth $d_\downarrow$ per query as

$d_\uparrow = \max\!\left\{1,\; d_\uparrow^{(0)} + \mathbf{1}[\ell(v^\star)\ge\tau_{\text{high}}] - \mathbf{1}[\ell(v^\star)\le\tau_{\text{low}}] + \mathbf{1}[\Delta>\gamma_{\text{high}}]\right\},$

$d_\downarrow = \max\!\left\{0,\; d_\downarrow^{(0)} + \mathbf{1}[\ell(v^\star)\le\tau_{\text{low}}] - \mathbf{1}[\ell(v^\star)\ge\tau_{\text{high}}] + \mathbf{1}[\Delta<\gamma_{\text{low}}]\right\},$

where $v^\star$ is the highest-scoring dense seed, $\ell(v^\star)$ is its hierarchy level, and $\Delta = s_1 - s_5$ is the top-vs-fifth dense-score contrast. A high seed level or large $\Delta$ increases upward depth; a low seed level or small $\Delta$ increases downward depth, with floors of $1$ and $0$.