Flat frequency targets suit binaural audio while Harman suits stereo

Evidence

The flat target was preferred for binaural content and the Harman target, for stereo content. Personalized headphone equalizations produced the highest preference ratings as did binaural content, although the trends remained the same. The effect of content on preference was smaller for the non-individualized calibration. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1862

Categorization

• XREF: Refines the Harman-target preference findings from earlier chapters; the target is content-dependent, not universal.
• QUESTION: Why does the preferred target shift with content type — is it about spectral cues that binaural rendering already provides?