I agree that a lot of factors go into this. My experience over the past 2.5 years of coming to terms with my enjoyment of pipe tobacco go like this:
1. Of course bowl size is the main factor but also the least important when it comes to your own expectations of enjoyment.
2. Are you enjoying the experience?
3. Did you pack the bowl well enough to enjoy the experience? Too loose and fast? To tight and wet? Too many re-lights?
4. Smoking speed, too fast and not paying attention to the act of smoking?
5. Is it still burning well but getting too strong as you get closer to the end of the bowl? Don't be afraid to stop, throw it out and look forward to your next smoke.
6. think a break will help if it's becoming too strong of a smoke half way through the bowl? Set it down and come back to it.
7. Still too strong and maybe wet? Remove the ash into the ash tray. Remove the remaining tobacco from the Pipe and let it dry. Maybe just stir the baccy up after the ashes are removed and allow it to dry while it's still in the pipe and try again later.
8. Heck take that last bit of baccy in the bowl and wait until it is bone dry and I'll bet it will still put hair on your knuckles because it will be still be a strong smoke.
In the end the only thing that really matters is that you can make a bowl last as long as you are willing to. But most importantly just remember your act of smoking is purely based on your choice of how to achieve enjoyment from it. Doesn't matter if you toss out half the bowl or smoke it down to the very briar.
I've heard smoking briar gives bad dreams and creates a back door into the spirit realm though. I would suggest just smoking the the tobacco as intended and find the entrance in the direction you are gazing into while doing so.
Throw it all up in the air and find the peace you are looking for. Dont run. It's your road, walk it yourself and be grateful for those you meet along the way. And you are on that path.
But all fun aside, Don't worry about long it should last.
