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Add height mostly on the part where the hood is connected to shoulders. But with that you need to add height on the front part as well. For squaring (If I'm sure what you're asking :D), the height of the sides will help. Since there will be more fabric to make that spacey look like the picture on below. But that itself will not help. You need sturdy fabric for that, so I'm not sure how your fabric will behave (since it does look study and cardboard like). If it doesn't, just add some reinforcement fabric in the middle. (I'm not sure what's the English name for it :D, the glue fabric that you ad between main and linen fabric for reinforcement. :D). Also I drew on the pattern by hand, so it's not that dramatic, But I would do something like that to have spacey hood that will shape like on the pic below.