Moving to the left or right of the sweet spot still gives you good sound stage and has less of the effect of sitting in front of a speaker with the sound coming right out of the speaker. Still the best three dimensional sound stage will be heard from the center seat.
Increasing your vertical listening height has little to no effect until your ear level reaches the top or bottom tweeter. Then the highs will begin to drop out. It's a physical limitation of all line sources. The effect is slightly less the further back that you are, but you still want to stay closer to the middle sections of the array if possible.
I hope this is not too much of a topic hijack, as part of the reason I asked about being close(r) to the speakers was because of the following:
I am in the lucky position of being an RSL II beta tester. I also very much appreciate the qualities I hear about your LS6/9 design, and would like to use those for music and HT next to the RSL II's.
Because space and money is limited

I might buy a pair and use those for surround/rear duty for the time being, waiting on the LS-center and -surrounds. I can toe them in in a nice way so I can switch them to mains in the "2nd room"-mode while sitting elsewhere. aa
The front baffle of each will be about 5' away. Would you strongly advice against using LS6/9's in such a way? (=as surrounds/rears)
Of course the fronts and surrounds/rears should sonically match also, but this is an interim thing. I could also place them next to the RSL II's and use my RSS300's (or some RS850's) for the other channels.