...Of course, all of this is academic if you use Rockwell's IAB software, which will work all this out for you and tell you exactly what you need. Though it's still useful to know, because in some cases IAB might tell you that you need another rack with an expansion cable and PS for a particular configuration, but if you understand the limitations, you might be able to rearrange your rack to put the low distance rating modules closer to the PS and get it to work with a single rack.