Do you have any screenshot examples to show exactly what you mean?
The light attenuation model is uses an easing function to soften the area where the falloff occurs. You could edit it in the shaders to use another easing function.
For example, in the fragment shader of shd_light_ss_hlsl on line 189 the easing is done by:
float edge = sin((1.0 - smoothstep(focus, radius + 1.0, light_len)) * M_PI_2);
You could keep just:
float edge = smoothstep(focus, radius + 1.0, light_len);
That would remove the easing and might get what you want.