Questions like this are some of the most common. Everyone would like a NUMBER (be it depth, height, speed, angle, profile, damage level, crew level, game year, weather condition, distance to target, ad infinitum) that guarantees success every time.
There are enough factors in the game and most of them salted with skill and random elements that it's impossible to remove all risk from your decisions. One day in an attack a tactic works and a few days later in another similar attack the tactic doesn't work. This is part of the suspense of the game. Every moment you are forced to judge risk based on the value of the target, your personal experience, and the conditions listed above. What a game.
The short answer:
It's great to be able to raise your profile to overcome weather and sighting conditions. How much should you do it? What can you get away with? As in all things, you have to moment-by-moment weigh losing sight on the target 40,50,60% of the time against being seen. On top of that, being seen isn't always a bad thing if you are close enough to get fish off that cannot miss.
-Pv-
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