i've heard at least 2 coaches say that you would get greater rhs on the serve if you tilt your head down just before contact because of the relationship of the neck muscles and the cartwheel action and this gives more flexibility at the end of the stroke. ... or something along those lines. I believe Heath Waters was one of the people that said that.
Yonex VCore 100s - SW 351 6pts HL
Tour Bite / Luxilon 4G 16 @ 51lbs