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Detectivity optimization of large-area freestanding-type YBCO superconducting bolometric detectors is theoretically and experimentally investigated. The effect of the device thermal parameters on the theoretical total noise-equivalent power based on background radiation, thermal fluctuation, and Johnson noise is considered. By analytical optimization of the total noise-equivalent power (NEP) of the device with respect to the thermal parameters and radiation modulation frequency, the maximum sensitivity and optimal thermal parameters of the bolometric detector are obtained. Relating device thermal parameters to the special case of the large substrate dimensions, the optimum device geometry is calculated. In addition, several devices with different geometries are fabricated to experimentally test the analysis. By performing experimental optical responsivity and detectivity measurements for these devices, the effect of the geometrical parameters on the maximum sensitivity of bolometric detectors is also empirically obtained. The analytical and experimental results are compared and presented in this paper.