Scaling primitive collisons

Hello, so when i open a mesh and put on the mesh primitive collision boxes and start scaling them to the mesh, the snapping and scaling just doesnt want to fit the mesh.
Its either too smal


or too big

I put the scaling option to 0.03125 but that doesnt have any effect when scaling option is turend off as the 0.0315 is still way to big of a scale gap. Its really frustrating and annoying. So if anyone has a solution to this i would be really grateful.