I cannot do multi-line in a comment, so I will demonstrate here.
In the following examples, distance(x1,x2) == distance(y1,y2):
+
|\
+-+
+
|\
| \
+--+
+
|\
| \
| \
+---+
With the rules as explained, distance(x1,x2) == distance(y1,y2)+2:
+\
| \
+--\+
+\
| \
| \
+---\+
+\
| \
| \
| \
+----\+
