Well, I'd have to say that the difference has to do with differences in mash efficiency and batch size. I know BCS uses 6 gallon batch size and 70% mash efficiency. I think BYO uses 65% mash efficiency. I'm not sure what size batch this recipe is for. If you want to brew one of these, I did the BCS recipe and it turned out great. Basically, if you know your systems efficiency, just use enough grain and sugar to get the percentages and IBUs stated in the recipes. Really focus on fermentation temp control and pitch using really healthy yeast and the proper amount of yeast. Good luck!!