Hate to amitt it but YOU are right. Temp for one might not be same as temp from all. Heck I cannot find anything easy to do, guess I will change DP again as that is getting easy for me the more I do it.
In a round about way, I figure, the best way to use an EGT on a motor with cylinders... is to tune to the leanest cylinder. This is the one most prone to damage. The Up Pipe is the best average, I have also read the hottest point?! And a good constant.
However, I would start with a "power plate" to "tune" air flow and even things out. Then using a band style "probe" determine the most consistantly lean cylinder. Drill and probe there.
Personally, I am going to drill and tap probe bosses into each header tube, plugging up the unused ones. This is for later endeavours using an EGT that can switch between probes from the "****pit".
In a simple means: With the Power Plate installed and a single probe in the Up Pipe... you should be alright.