  The {\it Kepler} mission revealed a population of compact multiple-planet
systems with orbital periods shorter than a year, and occasionally even shorter
than a day. By analyzing a sample of 102 {\it Kepler} and {\it K2} multi-planet
systems, we measure the minimum difference $\Delta I$ between the orbital
inclinations, as a function of the orbital distance of the innermost planet.
This is accomplished by fitting all the planetary signals simultaneously,
constrained by an external estimate of the stellar mean density. We find
$\Delta I$ to be larger when the inner orbit is smaller, a trend that does not
appear to be a selection effect. We find that planets with $a/R_\star$<5 have a
dispersion in $\Delta I$ of $6.7\pm 0.6$~degrees, while planets with $5 <
a/R_\star < 12$ have a dispersion of $2.0\pm 0.1$~degrees. The planetary pairs
with higher mutual inclinations also tend to have larger period ratios. These
trends suggest that the shortest-period planets have experienced both
inclination excitation and orbital shrinkage.
