Seatposts and stems (and everything else on a bike) aren't omniscient -- the manufacturer had to take a reasonable stab at how much length would be enough to keep from damaging the part or most frames in use.
Those of us who like to work it out for ourselves will want the seatpost to extend completely below the junction with the top tube, and having one seatpost diameter beyond that should be plenty. Some frames have a fair amount of seat tube extension above the top tube, so IMO it's good to think about this even if you weren't trying to cut anything close!
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Originally Posted by
chandltp
There's no such thing as too far.. just lack of time
Originally Posted by noglider
People in this forum are not typical.
RUSA #7498