I think this can be handled with any of the bel:-

(1) Providing Optimal icons in the web app manifest.

(2) Placeholder splash in your application :- Create a custom in-app splash screen that mimics the browser’s splash screen.

(3) Fallback Approach :- If precision is critical but measurements aren't exact Try doing transition your animation from a larger generic icon that fades/scales down to the estimated size based on the screen.

This are the approaches which i thought would work, though i never tested the same, or implemented this way before.