Thanks, @Thodoris, a very close reading of the User’s Guide that is pictured above suggests we may have taken a similar approach to what you describe.
So the REI_VX values are the average of the highest 10% wind speeds measured across the entire 22.5 degree sector. And the V10PCT_X are the average of the highest 10% wind speeds measured across a narrower slice (5 - 10 degrees) from the center of that 22.5 sector?