The "fill proportionally" distribution type works with the size of its own content .
Thus, if our vertical stack (height says 600) has 2 types, ViewA (height of internal content 200) and ViewB (height of embedded content 100), the stack view will be their size ViewA (height 400) and ViewB (height 200).
Besides,
- If all views do not have an internal content height, the vertical stack view will always display an IB error: "Requires constraint for: Y-position or height."
- Views without internal height are reset to zero height.
- Views that have an internal height will be distributed proportionally.
What do you really want
is a distribution of type 'fill' with two constraints.
- ViewA.height = 2 * ViewB.height
- ViewB.height = 0.5 * ViewC.height
That's all. Hope this helps.

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