In my initial post I had written that "You can also drive the slider with a function (click on the lightning) and then you have complete control.".

And in the manual, page 311, you can read:
"If you click the Drive with a function icon ( ) for the “Maximum angle” setting, you can control
the exact angle of rotation that is applied to each instance in the EcoSystem population. When this
parameter is connected, there is no more randomness in the angle of rotation. Expected values are in between -1 (-180°) and +1 (+180°)."