It would seem that no matter what, the VP180 and its location may turn out to be an insurmountable problem. What could be another alternative and if you are still within the thirty day return period of this recent purchase, you could replace the VP180 with one or two M2s or M3s as your center channel, especially if the mantle is your only option. This will give you somewhat more flexibility for placement without most of the weight and size issues to deal with.
I myself, have always preferred this setup since, in my opinion, the sound is more natural with better dispersion than any horizontal model.
Another good suggestion
