Most likely this QEX study considered only the NEC far-field pattern at an infinite distance over an imperfectly conducting, flat ground plane. Of course, this is not reality.
The radiation actually launched
by all monopoles of 1/2 wavelength and less always is maximum in the horizontal plane, and less than that at all elevation angles above the horizontal plane -- regardless of the number and length of buried radials and the conductivity of the earth in which they are buried.
The link below leads to a more detailed analysis incorporating the NEC4.2 near-field calculation, which shows the elevation plane radiated fields in uV/m at a horizontal distance of 0.1 km from a 1/4-wave monopole, for three different path conductivities (other things equal).
If "takeoff angle" refers to the angle where the peak field launched by a monopole is highest, then for monopoles of 5/8 wavelength and less the takeoff angle always is zero degrees.http://i62.photobucket.com/albums/h85/rfry-100/Monopole_Low_Angle_Radiation.jpg