Well, got the reply from the EE on my RFI suggesting their might be a code conflict. He said its allowed to run the IG separate from the other conductors. =\
So now my options are to do it the way he wants which is a code violation. Or run the ground wire back through the sub panel feeds.
Unfortunately the feeds for C1 are 2 2" conduits with 4 4/0s. Adding a #6 to each of these has an area of 368 mm^2, while 2" is allowed to only have 366 mm^2 (40%).
So my options are, do it the way shown on the plans. Add the ground to the parallel runs and slightly exceed code. Or eat the cost on replacing our 200' 2" runs with 2 1/2".
I think I'm going to have to do what the engineer says, I've done my job and pointed out what I think is not correct and he is standing by it.
