Bourbon Characters changing over time

In general, how do the Bourbon notes of a bourbon barrel aged beer change over time? Do they become more prominent, fade away, or not really change much? As Ive been drinking a couple beers lately, its seemed to me that the fresher the beer is, the strong the bourbon characters. I base this mainly off two experiences. The first being slowing drinking KBS over the past year. I have one every 4-6 weeks or so, and it seems to me that the bourbon presence has weakened thoughout the year. It may just be my palate variation or getting more used to bourbon barrel aged beers, but maybe not. The other is MoAS. The major flaw with this one is that Im comparing two different vintages, so there could certainly be batch variation, but the bourbon characters in the fresh 2012 bottle are so much bigger than they were in the approximately 8 month old bottle of 2011 I had. Just wondering what other peoples thoughts/experiences are.