I looked at it closely and it appears that KouLeifoh made the High Poly head compatible with default/vanilla Skyrim femalehead textures, which have this deformity. I suspect this is to maximize compatibility with existing texture mods (and those from the base game). The 'Enhanced Head Meshes' mod you mentioned makes the eye area of the head mesh more symmetrical, much as the ECE head mesh does. You appear to be using Fair Skin Complexion(https://www.nexusmods.com/skyrim/mods/51602) textures. If you look at that mod's requirements on the description page, you'll see this:
The face textures are most compatible with the symmetrical head mesh contained in the ECE.
With other meshes, the left eye area may look slightly distorted.
If you use those textures with a headmesh that is compatible with the default/vanilla UV, you'll have this issue. If you use a texture that is fully compatible with the default headmesh UV (e.g. Mature Skin) you won't have this issue.