It depends to some extent how close you'd like to be to the fire.

Is it a gas or wood fire pit? Wood fire pits put out a lot more heat and embers, so you may want to be a little further away. If it is gas, I like to be no more than 3 feet away because I like to put my feet up on the edge. In reality, I dislike seating walls. Real chairs are so much more comfortable if you are going to sit around with friends talking for hours.