Allegretto,
Welcome to the wonderful world of the 24mm Tilt/Shift. I have used one for years and, at one time, I had the full set of siblings (45mm and 90mm at the time).
Attempted to accurately place an optimal plane of sharp focus is something the requires a great deal of practice — the issue is NOT the lens but the 35mm reflex viewfinder. Perhapos live-view is a game-changer. I don't know because I have not had a chance to dabble.
I came to DSLR photography nearly 10 years ago after 40 years of large format view cameras. Lesson 1, page 1, paragraph 1 is that a tilt/shift does not a view camera make. (For all sorts of reasons.) It helps with the T/S and DSLR that I have an intuitive understanding of what is happening optically but it is still no walk in the park.
A good start is to get to grips with the fact that Depth of Field has nothing to do with altering the plane of focus and it is unfortunate that, for the sake of making sales simply, the camera brochures cloud the issue by applying incorrect terminology.
With regard to your alternative scenario, it is easiest to get a clear idea by realising that what you are dealing with is geometry — when you look at a scene you need to imagine lines through the scene and the angles of those lines and then start to set the tilt (or swing). I suggest some practice time playing with receding ground or walls to get a feel for what is happening and, quite often, how little adjustment is called for.
Best wishes,
W