I run 9.2, and love the front presence speakers. It does add to effects, and better fills the room with sound. Highly recommended. I didn't think much of the idea when I bought the receiver, but I did have the speakers. (I had a few DIY speaker projects that turned out pretty well.) You notice the sound coming from that direction. My A2010 has a 9 channel stereo mode, that takes advantage of them for music as well. I like it very much, it is a difference you can hear. The sweet spot is very big. (I did do multi-position YPAO, 5 spots). Walking through the room sounds fantastic.
I've experimented and set them (the presence pair) up as both Front and Rear presence (Yamaha's definition. The A2010 allows an 11.2 mode, but the rear presence and surround backs are used alternatively for effects, never both being on at the same time. I tried that, but it wasn't worth it, so I moved that pair to the bedroom to upgrade from 5.1 to 7.1 there.) The fronts I set up as in the OP's first description. As Rear presence, they were behind the surrounds, outside of the surround backs. Both were very nice, but my receiver supports the front presence better.
I'm currently running the mains, center, and surrounds off an Emo XPA-5, leaving the Yamaha 2010 to power just the Front presence(s) and Surround back(s). This room is about 15' x 25'.
Don't discount the addition for music.
I'll do 11.2 first chance I can get (it will require a different receiver to do that full time, and it's a fine excuse for another pair of speakers as well).
Give it a shot, especially since you already have the equipment. I'll bet you prefer it. I'm very surprised by the nay-sayers. Thanks to Adam for going against the flow for you. I agree highly with his advice, you should try it.