Hey there!
When you try to make the 8va hook length bigger, it doesn’t preserve the dashed style, as it does with the dotted one. I attach an image of an example seen in an Alphonse Leduc — Éditions musicales publication. It could be great that Dorico could approach this kind of style!
You will be able to make this adjustment for yourself using the forthcoming music symbols editor, certainly, but I will also grit my teeth and we will provide a proper option for this in future, though not in the coming update.