arrows use routing.arrow_distance=0; //turn automatic overlap avoidance off
a -> b;       //From the center of 'a' to the center of 'b'
a+x5 -> b;    //From five pixels right of the center of 'a'
a+x5+y5 -> b; //From five pixels right and down from the center of 'a'
a -> b-5;     //From the center of 'a' to the center of 'b' - but stop 5 pixels before 'b'