Hi,
I was wondering the same thing when I got my UM46k.
Check false color. If it is purple / blue, there is nearly no detail in the those areas so it can't take lifting. Green is middle gray and pink is one stop over. Yellow is nearly burnt higlight and red is burnt.
I learned a tip in BMCuser.com. I don't remember from whom it was, but thanks for the tip.
The tip was something like this:
On a sunny day - native ISO800 to get the best dynamic range.
Indoor, sunset, etc, when there is not that much light available. - ISO400 drops noisefloor down and you get cleaner shadows.
If you are shooting at night when there is almost no light and most of the frame is heavily under exposed (easy to check -> false color purple or blue) Shoot ISO 400 or even 200 to drop the noisefloor as down as possible.
My own observations when shooting like this (IMO):
First do your tests!
Light your images on location if possible.
Yes, this tip might sound little bit nonsense. But think it this way: How much underexposed areas do you have in your image? Is your point of attraction underexposed? If there is very minimal amount of underexposed areas then priority is in highlights, native ISO800 for best dynamic range. If there is a lot of underexposed areas in your image or your target is underexposed, you want to clean your shadows and there lower ISOs make the trick.
With RAW you can make it! It is more forgiving. Depending on situation, raw can easily take 0,5-1,5 stops exposure lift with lower ISOs and not showing that digital diarrea in the shadows. You can change your ISO in Davinci Resolve.
With prores it is more crusial to shoot like this because there is not that much room to play with and you can't change your ISO in post if needed. So if there is fpn it is there unless you don't crush blacks and lose detail in the shadow areas. If you shoot lower ISOs you can leave your blacks and shadows little bit "milkier" and have more detail there if you desire that look.
You could always lift your highlights and areas where there are enough light, but leave shadows down.
Luminance separation is handy for this (you can do this in Resolve and Lumetri)
If you need more light in the shadows -> add light to the shadows on location.
If shooting lower ISOs think like you are just dropping your black level and shadows in camera and you start to build your contrast and image from shadows to light.
Do your tests.
These are mainly my opinions and observations based on my tests, use and the method I found.
I hope this helps. Have a nice weekend!