They are set at that god awful angle because that's how Andrew Ritchey likes them. And it optimises the folded dimensions. Note also that the seat clamp is assembled in front of the seat post so a bit more reach can be achieved by turning it the 'right way round'. Brompton's recently released upgrade seat clamp is a thing of beauty and well worth the stupid money they ask for it. Not only but also; original plastic Brompton saddles are cheap and nasty, well worth upgrading. And.. they will soon announce the imminent release of a new OE saddle, I have no idea what it looks like but it can't be worse than the one it's replacing.