There's a container that holds that stuff. If you open the loot.xml file and search "backpack" there typically is a comment/note left by the devs telling you which container is for the dropped backpack. Now, I'm not sure about that mod, but sometimes you have to ALSO play with Easy Anti Cheat turned off. EAC will block use of a larger backpack and even if the backpack works, the dropped backpack can sometimes have issues with losing items despite having sufficient space in the expanded window. You'll need to do testing once you've found the container and made adjustments. Typically all you have to do for the container itself is change the dimensions, 6,5 to 8,10 type thing. Just make sure those numbers equal or are bigger than your backpack when multiplied.