Papazian has a Hop Utilization Chart in TCJOHB that recommends keeping your lbs of DME equal to your gals of water; i.e., 1 gal and 1 lb, 2 gals 2 lbs, etc., for maximum bitterness extraction.
Deviating from that one way or the other means you should adjust your hops. Too much malt equals a dense wort and low hop bitterness extraction, too much water tends to make not only more bitter, but gives it a harsh (versus mellow) bitterness, IMO.
I boil for 45 mins and turn the heat off. Then add 1 lb od DME at a time and dissolve it before adding the next pound. Then I let it sit for the last 15 mins.
I've been using this formula since 1994.