The recipe you are using probably assumes you don't have a big enough kettle to do that. There is nothing wrong with boiling the full volume. In fact, many would recommend doing so if you have the kettle capacity. There is an advantage to cooling the wort down when topping up with cold water...
Got some three Floyd's. Two sixers of zombie dust and gumballhead. I am in Chicago once a month and can pick up anything from three Floyd's for anyone. I live in Saint Louis so I can also get schlafly. Never had heady and would like to try.