So you are trying to tell me that the force exerted on lets say an 8" pour 4' high at the bottom of the form is the same as the force exerted at the bottom of a 24" x 4' pour and that the angle of repose has no bearing on that. You must have read that in some book I don't know about. Have you ever heard of a slump test? If the angle of repose had no bearing on concrete a slump cone would be irrelevant. As someone who has been placing concrete for 40yrs I will tell you that's wrong, concrete in its liquid state is not a pure fluid as the aggregate plays a part. And the aggregate based on the sharpness ( faceting ) and size affects the angle of repose.
That's what I'm telling you. The only time concrete thickness comes into play is when you are pouring a one sided form against a slope. The slope causes the concrete to move more horizontally causing more form pressure, verses straight down as in a form. Once again this is hydrostatic pressure we are talking about.
As for "hearing of a slump test" a cone test measures the fluidity of concrete, again we are dealing with liquid pressure. The slump cone is just a standerization method for measuring concrete wetness- again hydrostatic pressure.
You would be very hard pressed trying to find any mention of " angle of repose" in any concrete literature. Anything you may find will be referring to dry granular material, not concrete.
As for my experience, I am a structural concrete superintendent with 30 years experience with some of the most complex concrete structures in the Pacific Northwest, as well as a member of the American Concrete Institute. In a slow year I would still have placed 10,000 yards of concrete.
And I am writing a book on the subject.