[Craig T]

If you're going to mount any shelf required to support weight against drywall (i.e. trophies), you need at least 4" of vertical support below the shelf. Drywall is soft. Unless you have a rigid rod type mount at least 2" into the shelf and studs, and correctly spaced to the thickness of the drywall, a non-vertically supported floating shelf is going to sag.

I realize you want the clean look of a truly "floating" shelf, but that ain't gonna hold trophies against drywall with toggles or drywall screws.