The quantum sensor group at the National Institute of Standards and Technology (NIST) has developed the SLEDGEHAMMER (Spectrometer to Leverage Extensive Development of Gamma-ray Transition Edge Sensors (TESs) for Huge Arrays using Microwave Multiplexed Enabled Readout) hard X-ray and gamma-ray detector array (Bennett 2012, Mates et al. 2017). The array uses between 250 and 500 ∼250 0.38 mm thick, 1.45×1.45 mm2 footprint tin absorbers, thermally coupled to one TES. Each TES is coupled via a Superconducting Quantum Interference Device (SQUID) to a microwave resonator. A single microwave line is used to samples the response of the resonators of all pixels. The SLEDGEHAMMER array achieves energy resolutions of 50 eV FWHM (Full Width Half Maximum) over the 2-200 keV energy range. An assembly of one or several SLEDGEHAMMER arrays can be used in the focal plane of balloon-born and space-born X-ray and gamma-ray telescopes such as the proposed A Superconducting Energetic X-ray Telescope (ASCENT, Kislat et al. 2020), enabling hard X-ray imaging spectroscopic observations of astrophysical sources with unprecedented energy resolutions. We report here on tests of a SLEDGEHAMMER array with collimated 50μm diameter hard X-ray beams. The measurements make it possible to study the dependence of the detector response and the pixel-pixel cross talk on the location of the photon absorption. We will present the results from the measurements, and discuss them in the context of simple models of the thermalization processes following the absorption of the incident X-rays.