Dm, qm, z-dm- help pls

For floating rate bonds, we have DM, QM. QM + MRR gives us the rate we are receiving on the floating rate bonds whereas DM+ MRR is the rate used to calculate the Price of the Floating Rate.
My question is about Z-DM. So I got that Z-DM is the adjustment you add to get to the price of the floating rate bonds, but what I don’t get is how is it higher or lower than QM, DM depending on the credit profile of the bond issuer.
How can I visualize it to understand this properly?