Dry-vented sink enters branch drain question

I read in a pamphlet published by the Seattle/King County Public Health that a dry-vented sink can not empty into the branch drain pipe from right above, but must enter the drain pipe in the horizontal plane. Why? See the picture attached. Am I misinterpreting this? Just curious. Thanks. john

I would have to assume and interpret their logic as meaning that the non-compliant picture shows an offset in the pipe (90 ell) when the sink is serving as a vent for the branch. The offset is below the flood level rim of the fixture and that would make it illegal, even though it has a wash out (the sink) for the wet vented portion.
With that being said, the drawing is a poor example of code compliance since all of the floor mounted fixtures are connecting to the branch line via tees on their sides and the floor mounted fixtures that are downstream of the toilet (furthest fixture) must be individually vented.
Sometimes local jurisdictions misinterpret the larger, generalized codes and don't translate them well to the public.
Are you a plumber familiar with codes or is this a DIY situation?

I looked up your code king county

it clearly says to flat vent it, that is how we used to do it years ago, we never rolled anything
it sure made a 2 story rough easier.

Cad and frodo: thanks very much. that is how we are doing things so far. i am a diy guy, vaguely familiar w/ plumbing, as i have helped a plumber on a few houses. i guess the safest thing for a diy guy is to just vent everything and connect drains on the horizontal.