Spraying the spent grains in the mash with hot water to retrieve the liquid malt sugar remaining in the grain is called sparging. To prevent the mash from packing the volume of sparge water should equal the volume of wort being drained from the base of the mash tun maintaining a constant level. Maintaining the level of hot water above the grain bed help prevent oxidation of the tannins in the grain husks.
Ideally the volume of water, the sparge time and residual sugars in the mash tun come together to maximize the extraction and minimize tannins in the kettle. If you run too much water through, even if you don't get tannin extraction, you may have to boil longer
to get final volume you want and in doing so you may end up with more kettle caramelization than wanted. So forget the "standard 1/2 gallon of water per pound of grain". Vary the amount of water to suit your system so that when you've run all the wort out of the mash tun you should have a specific gravity reading of about 1.012 and the pH does not go above 6.0. So continue your sparge until your hydrometer reads 1.012, the pH starts to get close to 6.0, pieces of grain start coming through or the wort starts to get cloudy.