That makes perfect sense, Yooper. So I guess my real question then, is at what point does a change in the IBU/SG ratio become noticeable in taste (for most people)?
What I'm really getting at, is when I'm trying to follow a recipe, and I'm looking at gravities (pre and post boil), I want to have a feel for what gravity (ratio) I can say "I'll just leave it" and at what point should I should consider making a modification to bring it back in line. I think this will be less of a problem once I dial in my efficiency (it has been getting better and better each brew, so it's hard to predict at this point), but I think it would still be helpful for the future too, to have a gut feeling or rule of thumb on how much of an IBU/SG ratio change will be noticeable in the final product.