Correct... you will get the most accurate EGT reading if you mount the probe directly into the manifold..
Although, this causes a problem... especially for people that are basic BPU... they dont want to pull the manifold or fuss with installing something like this into something like that (

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Anyways.. people I have talked with about this same situtation say that whatever reading you get.. add an additional 100 degrees and that will give you a pretty accurate reading of the exhaust temp.. Asumming you are mounting the probe into the DP as close as possible to the turbos..
Obviously the farther, the less accurate...