To study the penetration of magnetic fields into ceramic YBCO samples and consequently local intergranular critical current densities, measurements of the complex AC susceptibility were performed, not only for different amplitudes of the AC field but also for different sample geometries. The experimental data are discussed in the framework of a modified critical state model. In the analysis it is taken into account that the position of the intergranular maximum in chi " depends on the Jc(Hi,T) function as well as on the sample geometry.