Yes, Rob and others are correct that Dorico cannot currently create a centred beam for notes all on one side of the middle line of the staff, or where the interval is smaller than a fourth. We have some tasks on our backlog to relax these restrictions, but I can’t say for sure when we will be working on this.
In the meantime, I think Leo’s right that you can produce the right result with a custom notehead set. The thing to be aware of is that when you move the ‘Stem up SE’ anchor point onto the wrong side of the notehead, you need to inset it from the edge of the notehead to account for the width of the stem, which will otherwise poke out to the left of the notehead. Take a look at the attached quick and dirty example. The two noteheads on the second space use the ‘Larger noteheads (stems on the wrong side)’ notehead set.
beam.dorico.zip (312 KB)