OPTXE is plotted in logarithmic scale across the diameter of spherical samples with radii a = 7.5, 10, 15 and brain-mimicking electrical properties at the corresponding magnetic field strengths B0 = 0.5, 1.5, 3, 7, 10.5, 14, 21T. OPTXE decreases for larger objects and as the magnetic field strength increases up to 7T. At voxels closer to the center, OPTXE increases again for magnetic field strengths > 7T, except for the largest sphere. Near the edge of the spherical sample, OPTXE is order of magnitudes higher than at the center, for all object sizes and field strengths.