Camera minimum exposure at 240 fps limited to 1/240

When using any AVCaptureSession.Preset the frame rate is ~30 fps but the exposure can go much below 0.033s, I often use 0.0005s to mitigate motion blur.

When I manually set the camera's active format to record at 240 fps however, the minimum exposure appears to be locked at 1/240.

Why is this?

I would like the 240 fps stream but using exposures much smaller than 1/240 to minimize motion blur.
Camera minimum exposure at 240 fps limited to 1/240
 
 
Q