Townsend's Quantum Mechanics Text Question

We’re using Townsend’s A Modern Approach to Quantum Mechanics for our QM class, and I’m just rereading Chapter 1 right now. Perhaps I’m reading too closely to the first section (in which, really, Townsend’s only aim is to motivate the theory and formalism for QM based on the observed deviations from classical theory in the SG experiment), but I’m bogged by the way Townsend ends the section (1.1). I imagine it’s just me not understanding classical E&M:

Incidentally, we chose to make the bottom N pole piece of the Stem-Gerlach (SG) device the one
with the sharp tip for a simple reason. With this configuration, $B_z$ decreases as $z$
increases, making $frac{partial B_z}{partial z}$ negative. As we noted earlier, atoms with a negative $mu_z$ are deflected upward in this field. Now an electron has charge $q = – e$ and from (1.3) with $g = 2$, $mu_z = (-frac{e}{m_ec})S_z$. Thus a silver atom with $S_z = h/4pi$, a spin-up atom, will conveniently be deflected upward.

Here is the SG setup he is alluding to:

I am interpreting the z-direction as up in the diagram, and the x-direction as to the right in the diagram. I believe Townsend is doing the same.

I can’t understand why he’s saying that "$B_z$ decreases as $z$ increases". From the diagram, it would seem that initially there is a large $B_x$ component, but as we move towards the S magnet it becomes almost entirely $B_z$ instead. It would thus seem that $B_z$ is increasing as we move towards the S magnet (ie. up in the z-direction)?

Also, as a slight side and classically speaking, do we expect that passing through a SG device should change the magnetic moment? That is, should the deflection of a particle with some magnetic moment upon entering the device change the magnetic moment vector?