if θ1 and θ2 are angle of incidence and angle of refraction respectively for a interface then according to snell's law ,
μ1sinθ1=μ2sinθ2
i.e, sinθ1∝sinθ2
θ1∝θ2
as the θ1 increases the refracting angle at 1st interface increases this results in decrease of incident angle on 2nd interface which in turn decreases the refreacting angle at 2nd interface i.e, θ2 decreases