It's not a terribly unusual growth pattern, one of the barber manuals mentions that most guys' beard grows downwards on the chin, sideways below the jay, and upwards on the neck itself. My beard generally follows this pattern, but I've got several cowlicks just below my jawline that makes shaving that area a bit "interesting".

For shaving the lateral hair below the jawline, I do something that sounds similar to xman. I shave the first pass downwards (across the grain), then flip the razor upside down and hold it about like you'd hold a pencil, and use a backhand stroke against the grain from the sides in to the center - I have to be careful here because there's a point where the grain changes direction and it's easy for the razor to catch on the whiskers.