Working backwards then, find the point 0.29 log-H left of 0.1 of the film-developed-to-ISO-conditions curve. Find slope of the tangent to that point and multiply by 3, do 1.50 times that, to find the density delta. Make a triangle with that density and 1.50 log-H and find where that triangle meets the curve.

What will I find? Will some of the measurement points coincide or be in a predictable place?

Or is it "Not locked down" and the Average Gradient triangle could wiggle anywhere depending on the shape of the toe?