Chris, IMHO, the short answer to your question is "no", the stripping guide placed slightly closer to the grip will have little if any effect on casting. I have seen custom fly rods that seem to work quite well with stripping guides only 6 to 7 inches away from the grips.
What I do to place the stripper guide is take the blank, once I've mounted the reel seat and grips, and "lazily" reach up the blank as if I were grabbing the fly line to cast. I then mark the place where my hand reached, and mount my stripping guide 1 to 2 inches up from that point. This method is not scientific, but it has worked well for me.
Hope that info is helpful,
Swamp