simple passes compositing issue Tweet

[gui2one]

Hi,
I have two simple passes : Diffuse and Reflection, and I am just trying to add them up in after effect. The issue is I don't end up with exactly the same image compared to the beauty pass.
I tried in PNG , tonemapped, untonnemapped, ERX, multlayer-EXR, all the same.

With only diffuse and reflection passes, the difference is not that big,( but definitely there !) , but it becomes very apparent when I use some atmospheric volumes.

Am I missing something ?