We had the Britax Marathon and he was really scrunched. Not just touching the seat but he could rest his elbows on his knees. It was just a bad fit. It wasn't until I read more about Britax experiences that I found out that they aren't usually the brand of choice for people with tall children since they tend to have shorter shells.
That being said, I ditched the Marathon and got a Clek Foonf and his feet barely touch the back of the seat. It's just a better seat for my kid in terms of fit, not to mention it's a heck of a solid carseat. For us, it was well worth the investment.