Hi Philipp,
I honestly have to admit, that this was something I had to try around with quite a lot because I don’t use this feature very often.
Grouping tools:
I am sure you have seen the grouping tools in your fixture view. The selection in the parameter control menu (as far as I have understood) is just a link to the grouping tools available. It therefore doesn’t matter whether you use the selector in the parameter control, the grouping tools window or the buttons in the fixture view.
Intensity works for you because it can be distributed (if fanning is enabled by grouping tool) Pan or Tilt can also be distributed across multiple devices. However, since we want to apply a FX across a selection of fixtures and curve follow is a boolean parameter rather than something that could be distributed across multiple fixtures, it does not work.
How to actually get what you want to achieve:
Now I am not sure this is the fastest way to do this, I would appreciate if @Matthias could verify or suggest a faster way to do this but:
You can select the whole group of fixtures you want to include in the effect, select your pan and tilt swing across all, select shape THEN use the grouping tools to block-select or Divide half of the fixtures and change the Mode (function direction) in panel 2 of FX.
Select all fixtures again and set the speed.
Some notes that could be bugs but I am just not sure whether they are:
-You cannot change the direction whilst lights are moving a.k.a speed >0, otherwise timing will be offset