Hello All. New to the forum, happy to contribute what I can.
I bought a pair of S.10's almost a year ago after removing a couple walls thus increasing the room size. Went from one smaller Rel to the pair of Sumikos.
I put them where I wanted them to be based on looks and educated guessing, tweaked a little, was happy with the outcome and have left them there ever since. I run them in stereo so each is dedicated to their respective channel.
My room is 23' wide x 25' deep, with a vaulted ceiling rising to 10-1/2' high. I easily forget they are there, which is a good thing. I simply enjoy how deep they can go and how natural everything sounds. Then there's what they can do for my Movie Nights, . . . . Wow!!
I've been very happy with this purchase, even with one issue that I haven't put any time into solving. If I use the Neutrik cable I get a faint hum. In the past with the Rel it turned out to be the Comcast coax that I needed to run through my power conditioner. I confirmed through Sumiko Tech Support how they recommend connection with my Krell amp, the hum is still there, but I really think the source of the hum is elsewhere in the system, I don't think it's the subs. I'll get after it someday. (The Krell is on its own dedicated circuit with isolated ground, the subs are each on their own dedicated circuits with a shared but otherwise isolated ground).
Hope this helps.
ttocs