You are missing the (probably exponential) decay factor on old posts, which must also include corrections for multi-sigma posts (Best/Worst Nodes live forever). $delta is really most strongly a function of your current "visible" nodes (things in Newest, Best and Worst) plus a hard to calculate function of citations in other Monks' "visible" nodes, based on those nodes' popularity.

$delta = $delta * &swag(now());
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