Quick questions . . who has the quick answer

So, I am going to brew my beer VERY soon and I have red over the How-To-Brew by John Palmer. I have also read the Northernbrewer. I am just stuck on one part. I have decided to pick up a 7.5 Gallon kettle and want to brew a full pot rather then using 2.5 Gallons of wort and adding in water to make 5 gallons. I was thinking . .
In NB's instructions it says to use 5.5 to 6 gallons in the kettle and to use 15% to 25% less bittering hops (any hop additions during the first 30 minutes of the boil) than called for in the kit inventory - e.g., use 3/4 to 7/8 oz instead of 1 oz; all other boil additions remain the same. Now, is this really necessary? Why would I need to use less bittering hops?

Also, the 15 - 25% less doesn't include the fermentables like the wheat malt syrup or the wheat DME, correct? Its only talking about the additions, like the 1 oz of Sterling that comes in the kit to be added at the beggining of the boil. (60 minutes)

Yes the 15-25% is hops only. Basically, bigger boil = get more bitter stuff from the hops so your beer will be overly bitter (or at least more bitter than the recipe calls for) if you do a full boil.

RDWHAHB...it's easy, you'll make great beer

You use less hops because the concentration of the wort is lower, resulting in more alpha acids in the hops (what causes the bitterness) being extracted when you boil them.

The 15-25% is only the hops. Everything else should be the same in the recipe.

If you do a full boil rather than a partial boil, then the gravity of the wort being boiled will be lower (because of the extra water). Bittering hops add more bitterness when boiled in a lower gravity wort than in a higher gravity, so you can reduce the amount of bittering hops slightly and still get the same effect.

The fermentables stay the same unless you want a lighter beer.

-a.

It's talking about hops only.

The concept is that hops are best utilized in pure water. If you boil them in solution with sugar, they are less effective. By increasing the amount of water in the boil while keeping the sugar constant, you are gaining a greater efficiency from your hops than planned in the recipe. So, if you want to follow the recipe and achieve the expected flavor, you reduce the amount of hops added.

It's not going to be a huge deal with a kit brew, though, unless it's a beer with large bittering additions.

You guys are soo fast! Honestly! Thanks for all the help ahead of time. I will be sure to post my result when i can!