Slitherine

Why do questions always spring into mind when you're at work and your rulebook is at home

If Artillery can shoot at troops 2 bases wide away from straight ahead at which point do friendly troops in front of them cease to block line of sight?

It's the same line of sight triangle, just drawn off to the side a bit rather than to the front, and any troops in the way at any distance block it.

Unless you are on a hill, then you can shoot over lower troops.