  Alkaline-earth iron arsenide (122) is one of the most studied families of
iron-based superconductors, especially for angle-resolved photoemission
spectroscopy. While extensive photoemission results have been obtained, the
surface complexity of 122 caused by its charge-non-neutral surface is rarely
considered. Here, we show that the surface of 122 can be neutralized by
potassium deposition. In potassium-coated BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$,
the surface-induced spectral broadening is strongly suppressed, and hence the
coherent spectra that reflect the intrinsic bulk electronic state recover. This
enables the measuring of superconducting gap with unpreceded precision. The
result shows the existence of two pairing channels. While the gap anisotropy on
the outer hole/electron pockets can be well fitted using an s$_\pm$ gap
function, the gap anisotropy on the inner hole/electron shows a clear
deviation. Our results provide quantitative constraints for refining
theoretical models and also demonstrate an experimental method for revealing
the intrinsic electronic properties of 122 in future studies.
