Soonami - what you are saying is pretty much spot on what David Perkins of High West was demonstrating to us this weekend. Young Blacksmith, David used the bell curve example exactly as you have. He brought samples of the first half of the heads to come off the still then the second half of the heads. Same with tails. We proofed it down so that it was potable and tasted them. There is no question that the "fingernail polish" distillants that boil early and are captured taste "hot". They also taste pretty nasty. However, when diluted .. you can .. much as when you get past the proof in any bourbon .. pick up on flavors. As David explained it, the amount of those "cogeners or contaminants" left in the barrel for years add to the overall flavor rather than detract from it and they are not there in enough quantity to make you ill. Certainly, if they were not diluted, they would be darn near deadly don't you think? As one of my old professors used to say: "The solution to pollution is dilution"!
Further to your point, Soonami, I asked David what kind of instrument he used to determine when to cut from the heads to the hearts, etc and he pointed at his tongue and simply said "taste!, it's still the best instrument when making good bourbon and rye".
BTW, almost everything David Perkins puts out for High West is bottled at 92 proof and some of them come on like a much higher proof tasting.