  In atomic force microscopy (AFM), the angle relative to the vertical
($\theta_{i}$) that the tip apex of a cantilever moves is determined by the
tilt of the probe holder and the geometries of the cantilever and actuated
eigenmode $i$. Even though the effects of $\theta_{i}$ on static and
single-frequency AFM are known (increased effective spring constant,
sensitivity to sample anisotropy, etc), the higher eigenmodes used in
multifrequency force microscopy lead to additional effects that have not been
fully explored. Here we use Kelvin probe force microscopy (KPFM) to investigate
how $\theta_{i}$ affects not only the signal amplitude and phase, but can also
lead to behaviors such as destabilization of the KPFM voltage feedback loop. We
find that longer cantilevers and modified sample orientations improve voltage
feedback loop stability, even though variations to scanning parameters such as
cantilever shake amplitude and lift height do not.
