Yes, I understand perfectly. I've created morphs tons of times.

OK. Here is what I did.  I loaded SydneyG2.OBJ into ZBrush. Entire model.  NOTE that this is NOT exported from Poeer. I actually navigated to the Included runtime:

Poser 13 Content > Included > Runtime > Geometries > PoserFigures > SydneyG2 / SydneyG2.OBJ

I created a makeshift Brows Up morph. Not the best as you'll see but it shows what I mean.  Then I exported it from ZBrush as Brow Morph.OBJ

I add Sydney to the scene. Then select the BODY actor and choose Figure > Load Full Body Morph.  I select the Brow Morph.OBJ file, and choose OK.

Now. You can check which body parts the Morph affects if you go to your Brow Morph in the Parameters palette. Then click the Right arrow near the Parameter dial and choose Delete Morph.  I dialog will pop up and show you the parts that got affected by the morph.

Notice that even though I used the entire OBJ to create the morph, the dialog only shows that three body parts were affected:  Head, Left Eye and Right Eye. That's because I accidentally moved some of the eyeball in addition to the head. 

So I uncheck everything and then tell Poser to delete the morph in the eyes, like so:

Now. Here's a before and after of the morph being used. Like I said it's not a perfect brows up morph because I didn't have a texture applied to the head in ZBrush to make it better. But at least this shows exactly what you are looking for: A morph that only affects the brows.  Here is the morph on the right, with dial set to 1. (You can set limits to make it go higher if you want).

When you save the morph target in Poser, ONLY the vertices that have changed are stored in the CR2.

As for the duplication of the morph and not being able to set two morphs higher than a combined total of one, the reason that is happening seems to be that you created your brow up morph with a custom figure. In order for a morph dial to affect ONLY a specific area, you HAVE to create your morph with the default SydneyG2.OBJ file as I said.  That way you can have your character dialed in to 1, and the brow up morph set to 1, and there will be no conflict.