We begin by illustrating that the spatial variations of the line - center Q / I and U / I signals of the Ly - α line are very sensitive to the geometric complexity of the corrugated surface that delineates the TR . Secondly , we demonstrate that the significant CLV of the Q / I line - center signal of the Ly - α line calculated in Carlsson et al 's ( 2016 ) 3D radiation MHD model of the solar atmosphere can be reduced by increasing the magnetic field strength and/or the geometrical complexity of the model 's TR . We then show how this can be exploited to constrain , from the CLASP line - center data , the magnetic strength and geometric complexity of the solar TR by applying the statistical inference method discussed inŠtěpán et al . ( 2018 ) . To this end , we confront the statistical properties of the CLASP line - center data with those of the polarization signals calculated in a grid of 3D model atmospheres characterized by different degrees of geometrical complexity and magnetization .