The properties of Josephson devices are strongly affected by geometrical effects such as those associated with the magnetic field induced by the bias current. The generally adopted analysis of Owen and Scalapino (1967 Phys. Rev. 164, 538) for the critical current, Ic, of an in-line Josephson tunnel junction in the presence of an in-plane external magnetic field, He, is revisited and extended to junctions whose electrodes can be thin and of different materials, i.e., of arbitrary penetration depth. We demonstrate that the asymmetry of the magnetic diffraction pattern, Ic(He), is ascribed to the different electrode inductances, for which we provide empirical expressions. We also generalize the modeling to the window-type junctions used nowadays and discuss how to take advantage of the asymmetric behavior in the realization of some superconducting devices. Further we report a systematic investigation of the diffraction patterns of in-line window-type junctions having a number of diverse geometrical configurations and made of dissimilar materials. The experimental results are found to be in agreement with the predictions and clearly demonstrate that the pattern asymmetry increases with the difference in the electrode inductances.