Photon counting spectral detectors (PCD) are being investigated for multiple applications such as material decomposition and X-ray phase contrast imaging. Many available detectors have fairly larger pixel sizes of about 150 µm or larger. The imaging performance is ultimately influenced by the choice of the sensor material, pixel pitch, contact type (Ohmic or Schottkey), spectral distortions due to charge sharing and pulse pile up. Several performance aspects must be optimal including energy and spatial resolution, frequency response, temporal stability etc. to fully utilize the advantages of a PCD. For any given design, understanding the interplay of various compromising features in the detector is very important to maximize spectral capability of these detectors. In this work, we examine spatial frequency performance of a small pixel PCD such as Medipix3RX with CdTe sensors. Measurements were conducted in single pixel mode (SPM) with no charge sharing correction as well as with charge summing mode (CSM) with built in hardware based charge-sharing correction, for both fine pitch (55 µm) and spectroscopic (110 µm) modes. While most of the simulations and measurements in the past use monochromatic x-ray to investigate these spatio-energetic correlations, our work shows preliminary results on these complex correlations when a polychromatic beam is used.