I understand the huge size difference is about sex appeal but we still need to follow a few rules so it doesn’t look too silly. When you go to art school one of the first things they teach you is that heads will generally be the same size regardless of other proportions.
This knowledge has unfortunately ruined a lot of Manwha for me lol.
A good implementation of a big size difference is with Jinx. Dan and Jaekyung are both VERY different sizes but the artist follows basic anatomy rules (heads and eyes are the same/similar sizes. Even babies have the same eye size as grown adults.
If you don’t follow these rules it will look more like The Titan’s bride rather than a big size difference (Although I’m aware that The Titan’s bride’s unnatural size difference is obviously intentional)