Mike, if the difference in contact area would really be sufficient to affect the final flavor profile, what about another factor that seems to have changed over the years, at least at some distilleries. I'm talking about the practice of rotating the barrels. Of course, moving from one part of the warehouse to another makes a difference; everyone knows that. But the very act of taking the barrels off the rick and rolling them to another location sloshes the whiskey around inside, ensuring that MUCH larger areas of contact are made. It also keeps the staves drying out at the same rate. The more often that happens, the more exposure all the bourbon in the barrel gets. By comparison, barrels that are left alone for years have essentially the same few surface inches in contact with the wood the whole time; the extracted flavorings reach the rest of the whiskey only by osmosis, and the charcoal filtration doesn't affect most of the whiskey at all.