The drawing of vertical wires does not appear to be increased, while the other orientations are.

https://cdn.discordapp.com/attachments/1310948834809085983/1310949014686007316/image.png?ex=674713e9&is=6745c269&hm=eb312e6df3c4eba25d2fe49d215b232cfa303837b918327db2797858b9c3c661&

I think it is an game engine limitation that nothing can be done about.

Yes, I raised this as a bug with the Factorio team a while back but unfortunately there was no momentum with it: https://forums.factorio.com/viewtopic.php?f=88&t=96231&p=538265#p538265

I wouldn't expect them to change the power line rendering just to support thicker wires, unfortunately.
As a product manager, if I would touch this part at all, I would update the rendering in a way that would make this mod obsolete.

For what it's worth, on high resolutions, this mod is a huge improvement already.