This is admittedly a ridiculously subtle use case, but the top of page 58 of Behind Bars recommends the following—
Dorico currently always places the dot in the lower space. Rhythm dots currently cannot be adjusted on a Y axis.
On the off chance someone is looking for a workaround for this, you can remove the dot from your desired note, add a dotted note in the same voice column one step above, then make it transparent. Personally, it’s too subtle a point to be worth the trouble, so this is just a heads-up.