This is an interesting topic as i had just fallen into the trap of doing Extract brews very early on, and asked for help.
Without a clue on the boil gravity concept, and without taking note of my total boil volume, i was putting too much malt in too early and also using too much liquid in the boil, and ended up with undesirable bitterness.
I would have thought there would always need to be some amount of hops on a 60 min boil to get any discernable IBU's into your final product, i had someone have a look at Beersmith for my last problem brew and the above problems were identified.
A 10 litre pot and 5-6 litre boils are all most people seem to need for decent results. (I also did a half batch as a cheaper way to practice!)
Following others recipes to a T is what i will do for a little while till i pick a few things up, i generally learn something each time i do a brew, i am onto Brew 11 now.....
Good luck
Mick.