How do I increase the Grease Pencil render quality?

I have various Grease Pencil assets – rigged & linked to the scene. And I’ve noticed that the quality of rendered Grease Pencil objects (detailing of lines, its "cubicity") doesn’t change – no matter what amount of samples I use for rendering. Have tried both Eevee & Cycles: 64 samples look the same as 4096 samples. The only thing that helps to achieve smooth and clear lines is rendering in 4K and downscaling the image.

Do GP objects use render samples in common way, like mesh for example (I’ve noticed that Cycles renders tile by tile depending on samples amount & resolution, and then GP just emerges at once – like it’s not being rendered, but just… drawn, added after main render is done)?
If not, how can we affect GP render quality?