Amy just came out of the jacuzzi. When your friend is posing with dripping wet hair, you better be quick with your photo. That's exactly when TTL for flash control comes in handy. I did set my Odin radio transmitter to ETTL, controlling a Mitros+ Speedlight inside a 60x90 softbox-umbrella. Snap-snap-snap... done. And off she goes to the hair dryer.
Pay attention to the histogram shown in the video. I marked the higher mid-tone area, which contains the tones that the flash produces on the subject. This is the portion of the tone you absolutely want to nail in your exposure. TTL is NOT a guarantee for getting these tones right, so try to keep an eye on them at all times.
I wish you good light!