One of the most common objections raised when someone suggests that Ricardo Allen has a real shot at the starting free safety job has to do with his height. "He's too short," is the frequent retort, and while that's an understandable sentiment, it's also a wrong one.
Earl Thomas, considered by many to be one of the finest safeties playing today, stands just 5'10". Ricardo Allen's just an inch shorter than that, and if he plays quality, aggressive football, that single inch isn't going to kill him. Even if he's unlikely to ever become Earl Thomas.
Quinn does like tall cornerbacks, and the selection of 6'2" Jalen Collins in the second round of the draft was a nod toward that end. But the Falcons also know that Desmond Trufant is an insanely talented cornerback with room to grow further, and even if he's "only" six feet tall, he's a fine fit for a system that rewards quality press coverage chops and aggression. Does that doom Robert Alford, who is under six feet but comes with legitimate ball skills and a really aggressive demeanor? No.
And that's really all I want to get across here: Height is not the determining factor for success in this scheme, and it's certainly not going to cost anyone their jobs. In an ideal world, of course Quinn would prefer to have a bunch of 6'3" proto-Shermans patrolling the field and delivering big hits, but that ideal world is years away, if it happens at all. For now, Quinn has to maximize what he is, and in Trufant, Alford and Allen, he has legitimate athletes with the talent to succeed. He wouldn't be a very good defensive coach if he couldn't look past how tall they are.
It's a game of inches in many ways, but it's easy to make too much of the two inches that separate Desmond Trufant from Tharold Simon, as one example. My advice is to worry purely about the talent.