How to specify an origin point to expand from in a prototype?

Hi there, thank you for taking the time to help!
It’s kind of hard to explain (no idea if the title adequately summarises it hah), so I’ll explain with context:

I’m prototyping a menu with several buttons that will sit at the base of the screen, and when one of those is selected a smallish popup appears with a menu.

The issue arises that, although my prototype works, the placement of it gets offset because the kind of origin point is the top left, expanding towards the bottom right (as is often appropriate). The goal for me would be to figure out a way to (functionally) make the hotbar a static base, and make prototype expand upwards and out from there once it shifts into the popup variables. I’ve included images to make the point easier to get:

Expected outcome:


Current outcome:


It’s possible i’m missing something obvious, I’m still new ish to Figma - but if you’re able to advise, that would be greatly appreciated.

Thanks in advance for your help :slight_smile: