Quote - Then it would be slaved to the morph dial in the conform target (e.g. v4), not the cloth figure itself.

No, that is not correct. With this method (no ":#") the slaving will always point to the figure that was selected at the time the pose was applied (providing the figure contains the target channel in the correct actor).

However, that is not always what you want to happen when applying a pose to a conformer. E.g. in the case of a JCM the slaving needs to point to the conform target, not the conformer.

The method works perfectly in any situation (at least in P6-P5, I doubt it changed) to do what you asked for, "target the currently selected figure in Poser, avoiding crosstalk issues". It's just that in the case of a conformer, the currently selected figure (the conformer) is not always the appropriate target for the slaving.

Quote - Is there maybe more control possible?

In a way, but not a very useful way IMO. Slaving code in a pose can target a specific figure, eg "head:3" or "hip:1", and Poser will respect that number, providing that it exists in the scene. But then, whether or not your slaving works as desired will depend on the loading order of the figures (first figure loaded = :1, second = :2, etc), and that is not a very satisfactory situation in my view.  

That was the problem with DAZ injections, their slaving targeted figure 1, so if you injected into figure 2, the morphs responded to FBM dials in the wrong BODY actor.

You are stuck with either targeting the currently selected figure, or targeting a figure with a specific figure number.