I don't have any experience with it, but I'm wondering if 44" doesn't give your rotary blade quite enough room to make a complete cut on the end? Maybe the blade bumps the end of the channel rather than completing the rotation?
Mathematically it sounds like it should work, but I can picture the fabric having to be positioned perfectly at the bottom of the ruler in order to give your blade the full 44". Again, no experience, just surmising.