Editing Mannequin - keeping hands only

Hello, I am to make a system like the shooter example, make 2 meshes, one with hands only and a normal one. I managed to do that however when I import the hand mesh, it’s smaller, so animations do not work properly. Like if I crouch and look below, the hands and gun go below the surface.

As you can see below they are almost the same:

but it seems like the hands are a bit lower. How can I fix this issue? I didn’t change anything in the bones, I only removed parts of the mesh.