4WD - what should slip first??

[Jac]

When adjusting your diff and slipper on a 4wd, what should slip first?

Should the diff be slightly looser than the slipper or vice versa?

I've heard conflicting information in the past so can anyone help!

To test; I stop one wheel turning, hold the spur gear and turn the opposite wheel. if the prop turns the slipper is looser than the diff, and again vice versa, if the prop doesn't move the slipper is tighter than the diff... right?

Thanks.