First consider doing:
{ StyleRef "Heading 1" } - { StyleRef "Heading 1" \l }
or
{ StyleRef "Heading 1" } through { StyleRef "Heading 1" \l }


Then you get:
"Chap 1 - Chap 2" or "Chap 1 through Chap 2"
"Chap 1 - Chap 1" or "Chap 1 through Chap 1"
which does not look as confusing.