Couple other factors:
Our wood dock has very long legs. As the dock comes out of the water the weight of the dock get heavier. As you say, the angle gets more favorable to help cancel this out.
As the cable on the spool builds in diameter, it takes more force on the crank to pull the same weight. Also in a favorable direction.
Lower angle gives the wind more leverage to twist the dock.
The water can get higher during the winter and ice can be pushed above the water level.
I have a pulley on mine so that I put two feet on the winch for every foot the dock cable moves. (Saves my back and allows me to use a drill for some of the cranking) But, the pulley reaches the winch which limits how far I can crank the dock.
Depending on the geometry of the pivot point and the legs, the angle to get above the ice can vary.
I usually stop when the close legs are about a foot above the water and balance my fatigue with the effort to repair the dock in the spring.
So far that has been fine. Probably about 35-45 degrees depending on which dock.
For some reason I much prefer lowering the docks in the spring at the beginning of the season.