Originally Posted by
lutz
The OP is in a different situation, as his seatpost is extended far out and because of his weight.
On my first bike I had to have 12-14" of post exposed because the frame was too small. My stock post snapped off after about 9 months. My Thomson is still in one piece. I have no experience with MTB posts, so I can't comment on that.
I'm not a cult member, but someone who lived through a seat post snapping off mid-ride and paid the extra $ to (hopefully) never have to experience that again.