Question Atlas Variant Scale for HD

Hello, I am making a mobile game and I have 4k size images in an atlas. I want to support FHD (1080p) and HD (720p) as well. However, downscaling mathematically from 4k (2160p) to HD is 0.333333, which is not POT.

As the value is very odd, every sprites in the atlas shifted and there are plenty of unavoidable white edges on the sprite.

Setting the atlas variant scale to 0.25 will fix the white edges but it will then make the sprites looking too blur on HD devices.

What is the recommended variant scale when I want to downscale from 2160p to 720p?