I believe the importance for a person to summerize his philosophy of life in one of his early chapters of his autobiography is pretty important. By placing his view of life in the beginning of his autobiography he is showing people what he believes and is preparing them for what might be coming in his book. Also, this could help the writer himself stick to what he has previously said and not change his beliefs throughout the book. But on the other hand, by putting his view of life in an early chapter his readers might decide they no longer need to or have a desire to finish the book.
In my view making it a priority to locate your philosophy of life in an early part of your autobiography would be the best decision. In any case I believe that as long as you stick to the same concept throughout your book it should be a success.