Re: Casting mechanics standing vs. seated?
Those are good observations about what happens when there is less room between the plane of your line and the ground or water.
When I teach casting classes here are a couple things I tell folks. When you deliver the line don't accelerate any differently than you do on a false cast. Its all the same--a nice smooth motion.
When I teach I have students start casting standing up. (We start in a grass field.) Then I have them sit in a chair to cast. From there I have them sit on the ground. Sitting on the ground is tough. Try practicing your casting sitting in a chair and it is likely your casting will improve both in the tube and from shore.