I play many different instruments of various types.

When learning the whistle, I was struck by how naturally it is a Bi-Modal Instrument.

If you play 'along the tube, the 'Authentic Mode' scale runs from 'all fingers on' - up one octave.

If you play 'around the corner', the 'Plagal Mode' scale runs from 'all fingers of bottom hand off' up one octave.

The whistle is easy for this, as the seventh of the 'Authentic Mode' scale is easily flattened, just by adding some fingers and keeping at least the top hole open.

On a C whistle the 'Major Keys - Ionian Modes' of C and G, for D whistle players, D & A.

"Each Plagal Mode begins on the Dominant, four notes below the Final of its corresponding Authentic Mode (but ends on the same Final as its corresponding Authentic Mode)."
from
FOLK MUSIC FOR THE VIOLIN LEARNER

I know I act the Foole a lot, but stop laughing, this is serious!

:-)