Flat notes are not deflated pitches. Sharp notes are not inflated or pushed higher. Flat notes result from the lengthening of the air column at the mouth. The mouth covers more or moves forward. Flat notes at phrase ends are the result of a collapsing embouchure and tightening throat.
Sharp notes result from a shortening of the air column at the mouth.
The mouth uncovers more or pulls backwards. Overall intonation is a product of the flute and its scale. Good intonation is a product of a stable embouchure that does not jump forward or backward when high and low notes are played.