Emissive deferred decal fades out

I have a very simple emissive deferred decal material: a grayscale texture multiplied by a color parameter. It was working as expected but after one of the recent engine updates they became only visible up close: when the decal gets smaller on screen it fades out quickly. Is this a bug? I can see it as some kind of an optimization except that it kicks in way too soon.

The decal component’s Fade Screen Size property controls this behaviour. Decreasing the value makes the decals hang around for longer.