Looks like if I used his recipe I'd end up about the same place that you would. Gravity errors with all-grain brewing are largely system based. Your system is more efficient pulling sugars out of the grains than the recipe accounted for. Most recipes seem to be in the 70-75% range (this one about 70%), and you're just over 80% efficiency, assuming that your postboil volume is 5.5 gallons. Lots of things that can cause this. The way you crush your grains, the way you lauter/sparge, whether or not you do a mashout, the temp of the sparge water, how far you sparge, etc.
Outside of a change based on gravity (higher efficiency for lower gravity, lower efficiency for higher gravity), if you find your efficiency is all over the place there's probably something inconsistent in your practice. But if your efficiency is consistent (at least at a given gravity range), then you just need to assume that for any all grain recipe you brew, and adjust the recipe accordingly. In this case, assume 82% efficiency and adjust grain bills accordingly (you'll typically need a little less grain than most recipes will list)