Most of the 5 gallon ale extract recipes I have made call for boiling 2 1/2 gallons of water to make the wort, then topping off to make 5 gallons total in the fermenter. If I was to try a full 5 gallon boil wouldn't I have to decrease my bittering hop addition since the bittering hops in the recipe were intended for a 2 1/2 gallon boil? How is this calculated? would it not make enough of a difference or be too bitter? Is it necessary to adjust all hop additions or just the bittering hops? What are the advantages of a full boil vs a 2 1/2 gallon boil?