How does linked gems work?

Hello,

I am currently following this build:

https://pobb.in/hNF75WY_Txy_


On the body armour, spell echo is one of the gems

But when I use my ball lightning it seems like it's not procing?

It works when i move the echo gem right next to orb of lightning.

All of my socks are linked (colour is exactly like the pob guide)