It won't matter much which
fixture you use if the other lights are spilling all over the back wall, and that has nothing to do with which
fixture you choose to light the back wall. It is all about where you light the rest of the
stage from. The steeper the angle, the better the chance that the light will bury itself on the floor rather than on the back wall. Where the people on
stage are also makes a big difference; the further from the wall the better. Also, choosing instruments with framing ability, such as ellipsoidals or Fresnels with barndoors, will allow you to cut off all or much of the back wall.
Once you figure that out, you can pick the fixtures to light the back wall, or how to do so. In reality, the fixtures are pretty much the same. The one you have installed is really just three of the one you have otherwise attached together. This allows you to hang one
fixture and place three colors in it. You can get a wide range of colors by placing red, green, and blue gels in it as red and green make amber, red and blue make lavender, and blue and green make cyan, and the combination of all three makes a variety based on their individual intensities. You could use the single
cell fixtures to have a very specific fourth color, or to intensify one of the red, green or blue cells.
You can also use some ellipsoidals to project
templates on to the back wall to break it up and add a layer of dimension to it.