Investigation of the overall emission arrangement in the emission region for four long-period pulsars is conducted by comparing the differences between their observed and predicted profile widths. The observed profile widths are taken from results based on observations with the Five-hundred-meter Aperture Spherical radio Telescope, whereas the predicted widths are derived from the conventional viewing geometry. The geometry predicts a profile width defined by emission coming from all the source points along a trajectory that traverses within an open-field region at certain height. In contrast, the observed profile width corresponds to only the range of the same open-field region cut by the trajectory that is actually detectable to the observer, referred here as the observable emission region. Our results show that the observable emission regions tend to coincide with the open-field regions, and their centers also exhibit a tendency to align, meaning that the emission originates around the magnetic pole. We demonstrate that the emission structure is likely uniform in the open-field region at a large rotation period. The field lines are mostly dipolar, and the radio emission is confined within the open-field region.