Not flying yet so I have nothing to say about how successful my EGT install will be, but... After much searching here and talking to other builders, I installed them all the exact same distance from the exhaust flange and in the same clock position on the pipe. This was done in attempt to have them read the same in terms of relative values. Considering each exhaust pipe has the first bend in a different position, spark plug access and cowl interference, mine ended up being mounted about 2.25 inches below the exhaust flange. According to what I had learned from others, the further from the flange the longer they will last, the closer they are, the more "responsive" they will be to changes going on in the cylinder. Not sure how true that is.
I would think that you would want the smoke oil injectors to be at least some or quite a bit aft of the EGT probes.
Bevan