It's very strange and you have to loosen it quite a bit, but it does change angle. Not sure I can really describe it as it's been a while, but in general you need to loosen that one bolt enough (quite a lot) so that the "teeth" holding it in place come apart, change your angle, and then tighten. Make sure you mark the fore/aft spot with a marker or something as the seat will slide around with the bolt loosened

Personally it's a PITA system

Agreed on the PIA. Thanks a lot. Will give it a try.

Yep. Of all of my bikes, my BMC TM02 is by far the biggest pain to adjust the seat on. It took me a while to figure out how to change the saddle. I was looking for the typical rail holder adjustments and had a hard time even finding that bolt under the seat. I have a fitting tonight, so we will see if it makes the fitter cranky (although he is probably more used to it than I am).