Those arena tours are the 3 times I've seen Biffy as a headliner. City and Colour was the real bizarre exception and honestly, not one I was sold on. Architects were awesome though.
I've never been able to work out why he is considered a festival headliner. I think his music is completely unsuited to that environment. And I'm a fan, seen him a couple of times but couldn't imagine a headline crowd giving his music the respect and quiet it deserves.