Speakers along short or long wall

FWIW when you're thru tweeking with the RS meter just relax and listen for a few months. By then you will have the sound stage fully absorbed in your mind. Then revisit the positioning to tweek your sound stage even more. Move speakers about, no more than an inch or so at a time (after marking the original positions so you can move them back). Great set up usually takes a long time, much experimentation, and patience. Enjoy.

FWIW I don't think any test disc is really going to give you the information you are looking for if what you want to determine is on which wall to put the speakers. I think the difference between the two locations is, as much as anything, how you hear all of the reflected sounds. Most folks I know prefer using the short wall. Give it a try. BTW Rives is as good test disc for tones as any and its corrected for the RS meter. If you want to fine tune your set up or equipment find a copy of Depth of Image by Opus 3, its outstanding for that purpose.