Geometric calibration is an essential technique that improves the absolute positioning accuracy of synthetic aperture radar (SAR) imagery. Geometric calibration of SAR has recently been moving toward a field-free approach. Field-free geometric calibration leverages the consistency in positioning conjugate image points across multiple images to determine ground coordinates and geometric calibration parameters. Notably, when the number of available images is limited, field-free geometric calibration may present instability in determining calibration parameters. We conduct a detailed analysis of the various sources of error that can affect SAR geometric positioning. In addition, we introduce the concept of dilution of precision (DOP) to assess the accuracy of the obtained calibration parameters. When the DOP is less than 5, we believe the geometric calibration parameters to be accurate and reliable. We analyze the impact of satellite geometry distribution and calibrated image quantity on DOP. Out of the 18 YG-13 satellite images captured in the Songshan area of Henan province, 3 and 4 images were chosen for geometric calibration, resulting in 816 and 3060 potential combinations, respectively. Calibrated solutions are obtained for each combination, and combinations with inadequate assessment accuracy are filtered out based on the DOP. After getting the geometric calibration parameters from the solution, we compensate them in the positioning equation and compare the accuracy of the two checkpoints before and after screening. The findings demonstrate that the post-screening combination surpasses the pre-screening combination and achieves comparable performance to field-free calibration and cross calibration concerning image localization accuracy. The effectiveness of DOP in evaluating the accuracy of geometric calibration parameter estimation has been corroborated.