The incidence angle θ (in degrees) required to explain a given ratio between the observationally determined ﹩{ \mathcal R }﹩ and the predicted λ _B. The black dashed vertical line indicates ﹩{\lambda }_{{\rm{B}}}={ \mathcal R }﹩. The red dashed line indicates the angle of 5° required by the current IFS data. The green dashed line shows that for any value θ ≳ 50° ﹩{\lambda }_{{\rm{B}}}\sim { \mathcal R }﹩.