ijimmy--
Nocking point and centershot are critical of spine, FOC, and any variations within configurations, so yes, I would say they would in fact tune slightly different and have slight nocking point and centershot differentials. I always tune each setup individually and have for years now, so I cannot say how much the differential is. How much depends upon how different each configuration is. However, some may simply have a different impact point as you stated, again, different configurations tune differently with different peoples' styles of shooting, along with any differentials in weight, drag, etc, which changes spine. One person can induce more torque than another with varying grips and form, that is why you sometimes see one person take a bow and shoot a perfect hole, and another take that same bow and throw a 2" tear. This does get confusing, but I think everyone is getting onto the same page here.
Jerry-
You no doubt have a good system for you in which you feel comfortable. If this gives you the results you are looking for, by all means continue onward!<img src=icon_smile_wink.gif border=0 align=middle> I do feel as tho you will gain better groupings, and especially so at distance if you utilize the "apples to apples" (as you call it) method as opposed to the "comparason method", but that decision is up to you, no one is twisting your arm! (at least not too bad. <img src=icon_smile_wink.gif border=0 align=middle>) Good shooting, Pinwheel 12