Agreed with the above. Also, mashing around 5.4 pH is said to enhance hop character. Having slightly elevated Mg content is also said to enhance bitterness per Brunwater. I keep mine no more than around 15ppm. More is definitely not better here.
Edit - Also, bittering with a hop like Columbus gives an IPA the assertive bitterness you're looking for, whereas a hop like Magnum might give the same IBU number in software but taste much less assertive.