ACES setup in MtoA

[Calvin.Hubbard]

Hi everyone,

I have recently adopted the ACES workflow and have a couple questions regarding the setup.

I'm confused as to why when selecting mid grey "0.5" I get a value of "0.275" when unchecking "Color Management" in the color picker.
To my knowledge it should be a value of "0.214"?
Is this because my Mixing Color Space is set to "Output - Rec.709"?

I couldn't seem to find a way to change this either...

Here is preferences setup

I am using Maya 2019.2 / Arnold 5.3.1.1

Thanks,