We examine how an algorithm for localizing cylinders of arbitrary known radius is affected by errors in the radius knowledge. Reflection mode multi-frequency multi-bistatic configuration is considered. The problem is first examined in far zone, where analytical results can be found. Then, numerical results for the near zone case are provided and a procedure to estimate the cylinder's radius, if it is not known, is introduced. The expected behavior is tested against simulated and experimental data for both perfectly electrical conducting and dielectric cylinders embedded into a lossless homogeneous background. Numerical results of localization of objects embedded into a lossy half space are also shown.