When creating wide angle reef scenic style portraits, the idea is to show the subject in its environment. The technique that works well for me is to meter the background and set the exposure. Then determine the light needed to illuminate the foreground. So this style of image has two steps. Metering for exposure and lighting the subject.
In the image below is a turtle swimming towards me at a depth of about 40 feet. To create the image I pointed my camera upwards in the water column and metered the blue water & set that exposure. Then, I recomposed on the turtle and adjusted the strobe power and position. I angled the left strobe so the cone of light would intersect the turtle and not light all the water in front of the camera. Then, I set it to two clicks under full power and the right strobe to 4 clicks less than full power. This helped to provide a smooth transition of highlight to shadow from the turtles beak and right side. By manually, setting the exposure and power, I know what was done right and wrong and can improve.
TTL is very popular these days and does a good job communicating with the camera. For that reason the majority of underwater photographers use it. I am a bit old school and want to know what I am doing right and wrong so I can always try to improve.
It can get confusing when you meter on the background and then recompose to light the foreground. Never mind, leave the exposure as set and concentrate on strobe power and distance.