I found a solution to have at least the elemts at the correct position, however if you’ve a very strong distortion it’s not working 100%.
I added some params to offset the widget on y and x and also to scale it on y and x.
I recommend to use a material instance for the retainer because then you can adjust the values easily while playing.
To find good values I copied the content of the retainer and pasted it in a overlay and set the render opacity to something like 0.2, so it’s just overlaying but without the effect of the retainer. Then I can see both the curved widget and the widget without the effect to know where the buttons or other interactable elements are actually hitable. It also helps to have elements everywhere so at top bottom and center, left and right to align it perfectly.
If it’s stretched on one axis more as on the other axis it’s no problem because if you’re done you can scale the retainer box directly in the designer under render transform.
And another small tip. If your Blend mode is set to Translucent change it to AlphaComposite for a better quality.