What to look for: a string (or, at inverter level, a whole inverter) that reads chronically off relative to its own site's typical ratio, without following a fixed time-of-day band — that's the MPPT local-peak-lock / hardware signature, not shading (shading is already screened out here by construction: the window sits around solar noon, and any day touching curtailment or clipping is dropped entirely). The flag is symmetric: LOW (red) is the familiar depressed-output case, but a HIGH flag (blue) matters just as much — if most strings on an inverter are locked on a lower MPPT peak, the pooled median drags down with them, and it's the few correctly-tracking strings that read as outliers on the high side. A high flag is not automatically "the good one." Drill into a flagged string and open its detail to tell causes apart: a string sitting at a different voltage than its peers (current not simply scaled from that gap) points to MPPT local-peak lock; low current with near-normal voltage points to shading, soiling, or a wiring/connection loss.