You have been given a lot of good advice, but what you are doing is called extract + specialty grain brewing. The goal of partial-mash brewing is to derive a sizable percentage of one's extract from grain and then supplement with extract. Partial-mashing is a technique that is half-way between extract + specialty grain brewing and all-grain brewing. Partial-mashing was more popular when I started brewing due to the difficulty and expense of bringing 5-gallons of wort to a boil. The high-quality propane stoves that we take for granted today were rare from the time that home brewing was legalized through the mid-nineties, and large stainless stock pots were expensive due to almost all restaurant-grade cookware being made in the U.S. It was much easier and cheaper to bring 2.5 to 3-gallons of runoff from a partial mash to a boil on one's kitchen stove in readily available kitchenware, and then add extract during the last 15 minutes or so. The wort was chilled and topped off with pre-boiled and chilled water.