As says – I've read references to the BFe not having bottle bosses on the ST so that you can drop the seat post right out of the way. How far down can you get your (ahem) post on a Soul?

Not sure if it's the same, but my 410mm post goes all the way done on my large Simple.

top bottle boss on my large soul is about 30-31cm from top of tube.

On the large and medium, you can drop a 400mm post pretty much as low as it will go. On the small it will drop around 22cm, and some people have chopped their seatposts down to gain an extra bit. The key thing there is to make sure to always have 10cm of seatpost insertion at full pedaling height.

Just to add to CY's point on a small with a 400mm USE i always felt it was just a couple of cm not enough! never got round to chopping it though!