I see. Apologies for the misunderstanding.
Not sure how to solve this for all resolutions, aspect ratios and / or widget sizes. Widget components display their content on quads whose screenspace size will depend on many factors. Getting a screen space size of a 3d object is not exposed to BPs. And you will need this data for the calculations.
You’ll need to dig deeper into the engine. I had to do something similar a couple of times for aiming reticules and it wasn’t fun to work with. You can start with this perhaps:
https://www.ue4community.wiki/legacy/get-screen-size-bounds-of-an-actor-3u16cs06
This will give you the critical data for the screensize; you know the size of the widget component quad already. You would need to project it back to 2d while taking the camera frustum into account.
If there’s an easy way of achieving a perfect translation like this, I do not know it. It’s easy to do for a fixed size but seems like quite a challenge if you add just a handful of variables into the mix.