I tried playing with the position but in the end it doesn't really matter, the only way I found to make it work is to set overflow: visible on the component itself AND its instances when you place them in a view. That's it, that's all you need.
The component itself can be flex or coordinate, doesn't matter.
You'll also need to make sure its z-index is lower than what's under the dropdown, otherwise it won't cover it. Or, you know, just click this:
Don't worry about it.
Make the view as high as the base text field and button, something like 32px I guess.
On the root container, add a overflow: visible style.
Then make the options panel where ever you want, outside of the view's boundaries.
When you place your dropdown in a view, check the useDefaultViewHeight property, make sure the embedded view is the right height (32px), and add the overflow: visible property here as well.
Make sure it's on top of other components by clicking or setting a z-index style.
I'm trying to figure out if there's a way to make things simpler, maybe through css, but it's already quite simple.
The only way i see this working is with js, but its not that simple as just to ask the position. You'll also have to make sure the popup actually fits on the screen (if your button is on the bottom of the page ,you'll want the popup to open above...)
Its all really just to much work imho, when there already is a multislect dropdown