60 minute hop additions

I personally have noticed a more astringent type of bitterness when boiling bittering hops for 60 minutes as opposed to boiling for, say 45 or 50 minutes, even when a little more hops are used at 45 or 50 minutes to achieve the same overall level of bitterness. I have a very sensitive palate when it comes to any kind of bitterness (e.g. except for milk chocolate, I even avoid darker chocolate because of the bitterness, to the surprise of many acquaintances who are addicted to darker chocolate) and can definitely taste the difference, although I suspect that it might not be overly noticeable to most. I remember reading something about that many years ago, and since then have followed the general practice of not boiling the bittering hops for more than 50 minutes.