I don't have one of these R51 models but I can make a swag at the answer based on dimensions of the 2011 Pathfinders at this link.
https://www.iseecars.com/car/2011-nissa ... dimensions
The information listed has the cargo area length dimensions you already know, to the first and third row seats. The length dimension to the second row seats is missing. However, there is capacity information for all three cargo area configurations. The information indicates a cargo box area height but the width information is variable and indeterminate, I've assumed due to rear wheel well protrusions primarily. There is enough information there for me to estimate the cargo area length to the second row seats is between 47.6" and 49.5". This is only my best guess. I really need to get a hobby.
