Do Dungeons Party Scale if Members Aren't in the Dungeon?

I’m confused about how Dungeons work with Party Scaling. I know that mobs in Dungeons have their life and damage scaled according to the number of players in the party but what I cannot find confirmation of is:

If I have 4 people in my party, 2 of us enter a Dungeon and the other 2 are off doing their own thing somewhere else, will the Dungeon I’m in be scaled as if there were 2 of us or all 4?

My group keeps arguing about how much more difficult Dungeons get when we’re in a group but we’re not sure if we’re just bad lol. Any info would be greatly appreciated!

They scale for the group size, whether you are in or not.

It’s easy enough to test, get 1 person have them stay out, next dungeon add another and have them both stay out, then finally get a 3rd and have all 3 stay out, you will clearly see the mobs need more damage to kill them, deal more damage and grant more exp.