Actually using chroma + lightness seems to work even better

web/metrics.js

@@ -5,7 +5,7 @@ const metrics = {
     displayBody: p => String.raw`
       \sigma\left(${p}\right)
       \Theta\left(${p}\right)^{
-        \sqrt{C\left(\left\{\vec{q}\right\}\right) L\left(\left\{\vec{q}\right\}\right)}
+        \left(C\left(\left\{\vec{q}\right\}\right) + L\left(\left\{\vec{q}\right\}\right)\right)
       }
     `,
     evaluate: () => 0, // calculated below
@@ -139,6 +139,6 @@ const applyMetrics = (data, target) => {
     Object.entries(metrics)
       .map(([name, metric]) => [name, metric.evaluate(data, target)])
   );
-  scores.alpha = scores.sigma * Math.pow(scores.bigTheta, Math.sqrt(target.chroma * target.lightness));
+  scores.alpha = scores.sigma * Math.pow(scores.bigTheta, target.chroma + target.lightness);
   return scores;
 };