The area of the intersection of the ray with the surface at A is greater than the area of intersection at B.

To a greater area correspond more atoms to reflect the light.

EDIT add

A justification:

The equations related to graphs on Steve answer (the reflected coefficients $R_s and R_p$) are the Fresnel equations when I read there $(n_1/n_2\cdot\sin\theta_i)^2$ I see a proportionality to the area.
The angles are in relation to the normal and sin² traces an area. A sensivity of the equations in relation to this factor should be done to prove the correctness of this answer. First one should convert $\cos\theta_i$ in terms of sin.
At the end I think, a priori, that my viewpoint will be validated.)

EDIT add end

the reflected rays are absent in the pic. Its not relevant.

The area of the intersection of the ray with the surface at A is greater than the area of intersection at B.

To a greater area correspond more atoms to reflect the light.

EDIT add

A justification:

The equations related to graphs on Steve answer (the reflected coefficients $R_s and R_p$) are the Fresnel equations when I read there $(n_1/n_2\cdot\sin\theta_i)^2$ I see a proportionality to the area.
The angles are in relation to the normal and sin² traces an area. A sensivity of the equations in relation to this factor is apparent in the graphs ($\theta_i$), because $\sin\theta_i, \sin\theta_i^2$ will 'follow' the shape of ($\theta_i$)
I think that my viewpoint is justified.

EDIT add end

the reflected rays are absent in the pic. Its not relevant.

![REFLECTION under two different angles][1]

The area of the intersection of the ray with the surface at A is greater than the area of intersection at B.

To a greater area correspond more atoms to reflect the light.

(the reflected rays are absent in the pic. Its not relevant) [1]: https://i.sstatic.net/FRzMm.png

The area of the intersection of the ray with the surface at A is greater than the area of intersection at B.

To a greater area correspond more atoms to reflect the light.

EDIT add

A justification:

The equations related to graphs on Steve answer (the reflected coefficients $R_s and R_p$) are the Fresnel equations when I read there $(n_1/n_2\cdot\sin\theta_i)^2$ I see a proportionality to the area.
The angles are in relation to the normal and sin² traces an area. A sensivity of the equations in relation to this factor should be done to prove the correctness of this answer. First one should convert $\cos\theta_i$ in terms of sin.
At the end I think, a priori, that my viewpoint will be validated.)

EDIT add end

the reflected rays are absent in the pic. Its not relevant.