I'm assuming that the lights are hemisphere in shape and have a diameter of 0.27 m.
Did the degree of front curvature come into your calculations? From photos (and dim memories), they seem to be slightly hemispheric (at the front). Also, does the shape of the rear of the lamps affect the degree of drag?
Also, is the pressure at the point where the lights are located the same as elsewhere on the fuselage? Do parts of the fuselage create a protective bow-wave or is this offset by AOA.