Seating distance to Magnepan 3.6r's?

I'm moving from my current living conditions to a new apartment. The main room (living room and listening room) is 17 feet wide by 26 feet long with 10 foot ceilings. My questions is: the Maggie's will be approximately 4 to 5 feet from the front wall, what is a proper listening distance, how far back should one's listening chair be?
Thanks for all your comments.