Hi si,
As you know, our engine / airframe / exhaust install was the same as yours.
While I am far from an expert, it seemed to me that the manufacturer suggested location was just that, a good suggestion / starting point. there is no way this number could be a 'one size fits all'. I mean the differences in engine and exhaust size, shape, configuration, etc, let alone potential cowling differences could vary what a probe is seeing easily as much as the inch further your going to have to locate that probe. Does a C65 put it in the same place as an R-1820? Or an open cowled Ag-Cat the same as a Lancair? I honestly don't know, but those are the questions that ran through my mind as I walked through this.
Since IMHO the EGT is a relative number to begin with, I valued quality installation first, equal distancing next, and either over the manufacturer's suggested location. I put them just outside of the slip joint. The one inch difference may have shown a slight reduction in temps (I highly doubt it) but it allowed for a better install. I believe that as long as those numbers fall within a range acceptable for a recip to be running at, you will be able to use them appropriately, and it would matter not if they say 1405 vs 1395.
I also believe that having them equal distance will lessen your work load in deciphering information such as which one peaks first or which one is colder, hotter, etc...
All of this information would still be available with probes scattered in a six inch range, you would just have to struggle with looking at each individual depiction and then processing that information against the others.
My opinion is worth about what you paid for it, but I haven't replaced a probe in the 10 years it's been set up this way, the information has been invaluable, and it has alerted me to issues on more than one occasion. I would not pony up for a $50K + engine without something like this to help you get as much life as you can out of it.
Take care, Rob