I just had the pleasure of meeting Jeff Galloway tonight- and got to pick his brain for 1 hour. He is such a nice guy so down to earth and offers up such great advice. Anyways, I asked him the same question OP asked.
I run an 11 minute mile ( just a normal not pushing myself hard pace). Jeff said for a half start out doing 1/1 ratio- yes from the very start because you want to start walking "before" you exhaust your muscles-
He also suggested for the first few miles to run at my long run pace which is your Magic mile x 1.3 plus 2 minutes.
After those miles he said you could switch it to 2/1 ratio, then around mile 9 or 10 you could run to finish if desired.
I wouldn't worry about feeling out of place- with the run/walk method in the last miles you will be passing all the people who started out too fast at the beginning of the race

Jeff also told me he runs at 11 minute pace and uses the 1/1 ratio for the
whole marathon.