Engraving options>Notes> Stems. I think the ranges indicated by arrows in illustrations ④ and ⑤ are wrong.
And picture below are correct illustrations , I think. (Note that these include the thickness of one beam.）
The current Dorico’s illustrations don’t indicate the actual stem length’s values correctly(In this case,④ 3 spaces, and ⑤ 2 1/2 spaces).
wrong stem length illustration.dorico (366.0 KB)