I've been trying the anchors McDave describes, and I shoot split. Seems to work well for me so far.
I didn't intentionally try to use these points as anchor references, but one day when things were clicking, I noticed my thumb knuckle touching my earlobe, and my nose touching the feather now and then. Practicing it now for a month or two.
Never occurred to me this method was more common shooting 3 under. I suppose my facial structure, and being used to a high anchor point already, contribute to its feeling pretty natural for me.
And as for the initial question - I fletch with three 5" shields, and feather placement is what I would call normal; a little over an inch from the throat of the nock. I do think about experimenting with that, if I ever feel like it would help with my alignment &/or sight picture.