Some glass looks invisible through other glass

This is working as intended. Glass is meant to be see-through. As a consequence of this, you can't see the edges of other glass blocks through the original glass blocks.

This is called 'culling', and prevents the texture from being too busy. It would look rather strange if you couldn't see entirely through all glass.

Why not just add the glass lines on the bottom?

WAI, see MC-34649