We should have a manual for that! Most of us here are, or have been, totally baffled about speaker positioning. I think a lot of the confusion comes from the audio industry's penchant for fuzzy language and failure to agree on common definitions and best-practices to define and instruct their customer base as well as installers, spokespersons about audio concepts. Other businesses addressed this lack of clarity long ago with major investment of time and treasure in programs such as establishing standards committees, six-sigma management programs, and the various levels of ISO900n certification that that required serious corporate navel-gazing and documentation. The result was that businesses were able to cut through and discard generations of corporate mythology, tradition, and redundant ways to do or describe the same processes, and to prepare procedure manuals to describe and train the best-practices for workers at all levels.
Speaker positioning is probably the most confusing part of this hobby for every one of us except for the headphone crowd. The help the OP is asking for indicates that he/she has no understanding of cause and effect in making changes to soundstage, frequency response extension, image size, etc. If there were such a list, we could read backwards from the bad effects we want to cure to find causes and take a corrective action that should be helpful in correcting the problem.
The audio industry sees no value yet in making this hobby more enjoyable for more people by reducing the frustration and aggravation that come from trying to do our own setups in our own homes by creating the kind of step-by-step procedure manuals to help us decide what to do when something in our systems needs to be addressed. We must rely on the collective knowledge of a disparate mass of people in the same boat we are in, some of whom may have knowledge that can help, all having "knowledge" that will not.
Fortunately for the OP, and others such as myself, who want to understand what moves to make in the speaker placement wars before we just start making random moves or worse, moving things around in reaction to every bright idea found on the internet, I have found a setup guide that describes, explains, and illustrates the cause and effect nature of all speaker setup geometry. In has 10 sections, each detailing a different aspect of speaker setup. Each section refers to a specific piece of music from a hi-rez file that can be used to adjust the single setup parameter that is its focus. The author is Gary Koh of Genesis, a veteran of many installations. This guy is the top dog at Genesis and is often involved personally in setting up his 6-figure systems in his customers' homes and theaters. There is no way this fellow is going to spend six months or more on site to just randomly move speakers around to get the job done and go home. He has taken the time to write up the procedures he uses in a format we can use for solving the same problems.
The white paper itself can be downloaded at: http://www.genesisloudspeakers.com/whitepaper/Genesis_Loudspeaker_Setup_Procedure.pdf
The same text is now embedded in the manuals that ship with Genesis' newer models, just before the specs at the end of the file:
http://www.genesisloudspeakers.com/ownersmanuals/G7.2f_Owners_Manual.pdf
Although the text was written to complement Genesis products, Koh writes quite a bit about non-Genesis speakers as well.
