Explanation about wave warp phase

Hello fellow users !

I need to set the highest or the lowest point exactly at the left side of my comp.
My wave width is set with a simple expression : W=thisComp.width/(effect("Slider Control")(1)*2);
If my slider is set on "2", it'll ge me 2 waves.

According to the AE reference : 
"Phase : The point along the waveform at which a wave cycle begins. For example, 0° start the wave at the midpoint of its downward slope, and 90° start it at the lowest point in the trough."

Weirdly, I need to set the phase angle to 64,6° ish to have my waves start at the lowest point. And -64°ish to have it start at the highest point.
Which isn't at all what's written in the AE documentation mentioned above.

Can someone enlighten me ?

I'll be much obliged.

Many thanks in advance !