In the so-called 'step-shape' angular spin distribution model for layered systems, the non-collinear directions of the atomic magnetic moments are confined to the film plane and form a homogeneous fan spanning inside an (in-plane) angular interval ∆ϕ centered at an angle ϕ₀. A general approach for deriving the two parameters ϕ₀ and ∆ϕ via ⁵⁷Fe Mössbauer spectroscopy measurements is discussed. The analysis extends our previously reported treatment, which assumed that the angular aperture ∆ϕ develops symmetrically versus a fixed direction ϕ₀ (e.g., the in-plane easy axis of magnetization) oriented either along or perpendicular to the in-plane projection of the Mössbauer γ-ray direction. The proposed approach is also applicable for those cases when not only the spin aperture ∆ϕ is changing but also the aperture center ϕ₀ is rotating under the influence of different external parameters, such as applied field, temperature, stress, etc. The method is suitable for applications to nanoscale layered heterostructures with in-plane uniaxial or unidirectional magnetic anisotropy. The method is applied to experimental data obtained on a 2-nm thick defected Fe layer with in-plane magnetic texture.