Very astute observation, Chucklehead!
The downwash from the main rotor is skewed by the rotation, and tends to press downward on the right horizontal tail more than the left (for a US rotation rotor.) This is especially true of helos with low stabilizers, where the MR wash is stronger than if the tail is high up. If you could see the column of air, it would show a sweep to the right and down as viewed from behind, at high cruise speed.
The asymmetrical downflow means that if you press right pedal and slide the tail under the left side if the wash, there is much less downforce. This makes the nose dive downward. Left pedal moves the tail to the right where the downforce is higher, so the nose pops up.
On some helos the pedal at high speed is as powerful a longitudinal control as the cyclic!