Empty scene won't achieve 90fps

Thanks for the reply.
Yes, this is happening upon covering the sensor (as if mounting the headset). Screenshot attached from the project I'm working with. I cover the sensor halfway through the visible histogram.
You can see the rendering, scripts (assuming that's the VR.WaitForGPU) and VSync jump way down to ~1ms when I cover the Oculus sensor. But interestingly, while the profiler always reads about 100fps, the OVRDebugInfo matches my custom FPS counter visible on the game window and is usually 80-90fps
So I guess my question is: Is this normal behaviour by design when the sensor is covered in order to provide 90Hz?
But if that's the case, why would it drop to consistently BELOW 90fps in my case? My submission feedback from Oculus is just "Your app should maintain a framerate of 90 FPS most of the time." so I can only assume it's this that they're referring to as I'm not seeing any other sustained framerate drops in my app.

Thanks.
Okay. But if Unity's profiler is telling me I'm maintaining 100fps when the proximity sensor is covered, but the Oculus Debug Info script is telling me I am getting 85fps at the same time, I don't know what to trust. I imagine that the store team are using the tool written by Oculus so I was understandably concerned about this.

In the meantime, a few days ago, I sent a request for more specific information to submissions.oculus.com because I can't identify a section of my app where the framerate drops dramatically for more than a couple of frames. I've not heard back yet, so I guess I'll see what they come back with.
If they say that it's consistently under 90fps then the issue is to do with what I've been questioning on here.

Thanks imperativity. I shall continue to dig deeper.