Luke-Acts or Luke–Acts and the Proper Use of the Hyphen

I found this article on proper use of the hyphen at The Chronicle of Higher Education more interesting than I probably should. I remember that during the writing of my dissertation, a serious discussion took place over whether it should be Luke-Acts with a hyphen or Luke–Acts with an en dash or en-dash (I have seen it spelled both ways). It was decided that Luke-Acts with a hyphen should be used when referring to these two books as a unity. But Luke–Acts should be used when referring to Luke through Acts as it relates to contact. That is shaving with mighty fine razor!