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A two-arm metaspiral antenna is presented, where the feeding voltage sources are expressed using excitation amplitude r and deviation angle δ. This excitation is decomposed into the odd mode and even mode components. The odd mode component forms a circularly polarized (CP) axial beam and the even mode component forms a CP conical beam, whose maximum intensity is off the antenna axis. Superimposing the conical beam onto the axial beam forms a reduced radiation region in the elevation plane. The reduced radiation region is used for minimizing transmission in a particular φ_FBD direction or the rejection of interference signals from the φ_FBD direction. This paper presents a formula that estimates the azimuth angle of the reduced radiation region. The formula features the excitation mode ratio, m, and the mode phase difference, ΔΦ. The formulated azimuth angle is validated by showing good agreement with the simulated azimuth angle obtained by searching for a null over the 3D radiation pattern. The formula is simple and hence supersedes the time-consuming 3D null search.