when you type this command in a command block and test it while looking west, and not down:
/testfor @p[rx=134,rxm=45] it will not find anybody, while it should.
However if you now look down, it will find you, because rx and ry are simply switched and act wrongly. as if y = x and x = y.
changing the command to:
/testfor @p[ry=134,rym=45] finds you as long as you are facing west, not as long as you are facing down.