Mick's diagram is a good reference. Attached is my interpretation of how your's differs from a more ideal geometry that Mick posted. Your upper outer point is further outboard than the lower outer point, plus (and the assumption is that the suspension has insufficient weight on it to force it into the static ride height in your photos) the upper outer pivot point is lower than the upper inner (due to the angled piece at the end of the upper arm plus ball joint. In my diagrams, the upper configuration is a static ride height, and the lower pair is at bump.
If my representation of your suspension is correct (and fully loaded), then it would indeed benefit you to move both upper and lower inner pivot points lower than they are now. If you only want to change one arm, I'd say lowering the upper arm is the best bet in that case. But again, this is solely based on what I can tell from the photos.