Is the head supposed to be underwater in freestyle?
No. One of the many misconceptions about swimming technique is that the head must be submerged for the legs to stay behind the shoulders and minimize resistance. A more effective way to minimize the body cross-section is to arch the lower back to bring the heels to the surface. Maintaining the water level just above the hairline puts the head in an optimal nonbreathing position that also minimizes the head motion necessary to breathe.
