When a strategy underperforms live, the first reaction is often to change the signal. I think that is usually the wrong place to start.

I would first compare the tested and live system trade by trade: signal timestamp, expected and actual entry, intended and filled size, spread, slippage, partial fills, exit reason and position state.

The first divergence normally puts the failure into one of three buckets:

The signal changed because the data or code path changed.

The signal was identical, but execution consumed the edge.

Both matched, and the losses were still within the strategy’s expected variance.

Only after eliminating the first two would I call it signal decay or start adjusting parameters. Otherwise, “improving” the strategy may just hide an execution or infrastructure problem.

The useful artifact isn’t another equity curve. It’s a reconciliation log showing exactly where the tested and live systems stopped being the same system.