The 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 Kepler and 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 .