Correct use of PostProcess Material Opacity

Hi, i want to use the alpha channel to encode the costume depth stencil, therefore i added a Post Process Material and enabled translucency and used the depth stencil as Opacity.
I have tried multiple variants (ie. different BlendModes and Blendable Locations) however in my final picture (I used a CustomViewportClient to get those) i will only have the value 0, 85, 170 and 255.
It appears that the alpha channel has only 2Bits. Is this correct and if so is it possible to change that? or am i missing something here.

Alternatively is it possible to use 16bit colors for the PostProcessMaterial?