Moving the flute cork changes the spectrum far beyond mere length effects

Evidence

The positions shown are outside the usual cork distance of 17 mm. The nominal frequencies of an open-open tube are fn = nc/2L, so the resonance frequencies certainly should decrease as L is increased by drawing the cork farther out. But the effect on the spectrum is much more dramatic than that. — Eric J. Heller, Why You Hear What You Hear- An…, 1577

Categorization

• XREF: Connects to the gatekeeper resonance concept developed for trumpet mouthpieces; shows the same principle reappears in a woodwind.
• QUESTION: Why is the effect ‘much more dramatic’ than the length change alone? The impulse-response explanation in the next paragraphs answers this.