What do you mean by “running per eye” ?!
FS2020 is rendering at a certain resolution, which is the one you set in the settings. In order for a VR headset to display every single pixel, you have to render at a higher resolution than the headset panels native resolution. How much more depends on both the optical properties of the headset and the VR API distortions applied to the rendered view, but also on your own perf/visual acceptable balance.
In addition, you can configure FS2020 to rendering a certain amount of pixels, and extrapolate “in a visually pleasant way” these pixels to a higher amount for the headset.
For the reason of rendering to a higher res than the panels, you might want to watch Alex Vlachos videos (links at the end of the OP in “My VR Settings” discussions). For the “visually pleasant way” please read “My VR Settings” posts for explanations about the CAS Shader.