I'm assuming your doing all grain. After mashing, you need to rinse the grain (sparge) to get the remaining sugar. If you dont, your leaving a lot of good sugar behind. A refractometer is a good tool to have during sparge. You can take readings as you sparge to determine when you've hit your sugar extraction limit. I like to stop before 4 degrees brix (1.015 gravity). On traditional Scottish Ale, they actually made a second beer from the remaining wort called the second runnings. It was a session beer (very low alcohol) and was referred to as a 2p (penny, the price of a pint) as opposed to an 80p.
All that said, IPAs require a certain malt level to balance out the hops. Another question is mash temp which takes us to a whole nuther discussion.
Have you read John Palmer's
How To Brew?
When do you sparge?
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