All human beings in general are able to sing higher notes using falsetto than head voice. In fact the term falsetto is Italian for false and the term is used to describe the ability to shift into "false" voice to achieve higher notes than you are otherwise capable. Although scientist believe that not all people produce falsetto the same way.
In order to sing higher notes, it is necessary to lengthen and stretch the vocal chords (like tightening a guitar string). The tighter vocal folds will vibrate faster and thereby produce a higher sound frequency. Every singer will reach a point where their vocal chords are at maximum length (stretched to the max).
But alas, there is a way to eke out a few more "false" higher notes by switching to falsetto. Falsetto allows us to sing higher notes because the action of the vocal chords is altered in a way that allows a different part of the vocal anatomy to vibrate at a faster rate than the maxed out main vocal folds.
When we switch to falsetto, the vocalis muscle relaxes allowing the cricothyroid muscles to exert more tension on the vocal ligaments. During the use of falsetto voice, the main vocal membranes are relaxed and a faster vibration is permitted to occur in the vocal ligament which has now been allowed to stretch tighter than it could before it was released by relaxation of the vocalis muscle.
This relaxation of the vocalis muscle also creates a situation where the vocal folds are not drawn together. Therefore air can more easily and freely pass across the vocal chords and vocal ligaments because you don't need the air pressure normally required to push through the vocal folds. Since less air pressure is required, you can sing high notes in falsetto at lower volumes.
If you are singing in falsetto, you will notice that you won't need to exhale as forcefully to sing high notes. You should also sense a relaxation in the muscles that control your vocal chords. You will also be able to sing high notes much more quietly when singing in falsetto.
