It does depend on the horse. My paint mare, I give her a little more room. My moms gelding needs a ton of room too, he's a big boy. My lease mare is only 14 hands. Honestly if I were to take her wider, I'd barely place because the turns are where I make up my time. She doesn't have a long stride, but she doesn't have to slow down much in her turns because of her shorter legs. I've only hit one barrel with her and it was my fault. I was fighting with her to set her up and couldn't get her where I wanted so I let her go. She dropped her shoulder before we even passed the barrel and got into the pocket.
Every horse has a different running style but I don't agree with the first drawing with the consistently spaced turns. But that's just me and my style. I prefer to go wide and come out close.