Proper Preference Settings for Multi GPU

Ok, I have 2 GPU's in my machine.
If I set Resolve to Auto in the Preferences, only one GPU is shown:
If I set Resolve to CUDA and Manual both GPU's are shown:
I am a bit confused as to why in Auto mode Resolve only shows one of the GPU's? Does that mean that in Auto Resolve is only using one of my two GPU's and the only way to use both is to set my preferences as Manual, or is it safe to assume that Auto uses both GPU's even though it only shows one of them?
If I set Resolve to Auto in the Preferences, only one GPU is shown:
If I set Resolve to CUDA and Manual both GPU's are shown:
I am a bit confused as to why in Auto mode Resolve only shows one of the GPU's? Does that mean that in Auto Resolve is only using one of my two GPU's and the only way to use both is to set my preferences as Manual, or is it safe to assume that Auto uses both GPU's even though it only shows one of them?