Kinda lame problem here - I haven't figured out how to attach this thing without it swinging around *lots* during the ride. The main strap seems to be attached to the pak upside down, but it's obvious from the seatpost strap what way it should be attached.

So the seatpost strap is fine, but I can't attach the under-saddle strap properly. Can anyone whos got one of these please attempt to explain what I need to be doing? Thanks