I played 'Cosmos LaudroMATT'
last night, and found that
peak HDR-DV bright is 18 with the Backlight according the the
bright center of the swirl at 8:08 into the short.
Moving the Backlight up, blows-out the bright and goes back
down after 30 (but remains a bit still blown-out) and stops going
down from about the 75-to-100 Backlight range.
If I stop the short and start it up again, the last Backlight number
I had set it to while playing Cosmos, is remembered and snaps to
that number, such as 18 or 75.
So it appear 75 is a happy compromise to tone down the peak bright
blow-out and yet have decent mid-tone levels.
If I leave it at 50, there's blown-out HDR peak-brights. I saw it in
'Iron Fist', also.