Although the Broncos signed quarterback Case Keenum in free agency, ESPN Draft analyst Mel Kiper Jr. still believes the Broncos won't pass up a quarterback with the fifth-overall pick in the upcoming NFL Draft.

In his third mock draft of the draft season, Kiper has the Broncos selecting Oklahoma's Baker Mayfield, arguing "Denver can't pass up a guy it thinks could be the face of its franchise for at least a decade."

Mayfield's astronomical production in his senior season (43 passing touchdowns and just six interceptions) earned him the Heisman Trophy and helped position him in the tier of top quarterback prospects. Yet in spite of those accomplishments, analysts still seem unsure of his NFL outlook. Few analysts — if any — project Mayfield to be the first quarterback prospect to come off the draft board.

Why that's the case may boil down to his height.

When measured at the combine, Mayfield clocked in at 6 feet and five-eighths of an inch tall. Meanwhile, each of the other three quarterbacks expected to be drafted in the top 10 — Wyoming's Josh Allen, USC's Sam Darnold and UCLA's Josh Rosen —were at least 6 feet 3 inches tall.

It's not the only factor, but it appears to be a big one. It can definitely create obstacles for shorter quarterbacks, as Kiper noted during a conference call with media Wednesday.

"[The question] is more, Can he throw through passing lanes and not have passes batted down?" Kiper said.

Because of that and because there have not been many examples of successful quarterbacks Mayfield's height or shorter who have overcome that, height issues at quarterback tend to scare off some analysts and other football minds. 

But there are examples otherwise, and one thing you can count on whenever people discuss Mayfield is those names — Drew Brees and Russell Wilson — will come up.

"Obviously there's been very few quarterbacks his size that have made it big in the NFL, but some have," Kiper said. "I think Russell Wilson emerging the way he did at [5 feet 10-and-three-fourths inches] bodes well for the body type of Mayfield, who's not lean. He's got that strong frame like Russell Wilson. The main thing is going to be, Can he continue to do what Drew Brees has done and what Russell Wilson has done and some other ones haven't been able to master once they're in the NFL?* *That's the unknown of being six-foot-and-a-half for Baker Mayfield."

Those two came up again when Head Coach Vance Joseph was asked at the NFL Annual League Meeting about the value of height when evaluating quarterbacks.

"I can speak to two guys that are playing currently [who have overcome height concerns] and that's Russell Wilson and Drew Brees," Joseph said Tuesday. "They've both overcome it with unique skill sets. Russell was a guy who is a great athlete. He can make guys miss in the phone booth. He's got a big arm. He's guy a high-arm release. Russell's release is really high. When he brings it up, he's probably at 6-1 when he brings the release up, like a basketball player. 

"And Drew just finds windows. Drew is like Peyton [Manning] and he's like Tom [Brady]; pre-snap he knows where the ball is going, so he doesn't have to find a lot of windows. He knows where the ball is going. He has quick feet. He gets back in his drop really fast and the ball is gone."

When asked if Joseph sees any similarities between Mayfield and Brees, he had one example, but it came with a caveat.

"That one trait that Baker has that Drew has is accuracy — historic accuracy in college," Joseph said. "That is what Drew has [in the NFL]. We won't know about Baker until he gets out there and plays. That is the story with these young quarterbacks. You watch them in the Pro Days and you watch them play college, but you won't know if they're going to be like a Drew Brees until they go out there and play against NFL competition, which is different than college competition."

Inserting himself into that class of quarterbacks with Brees and Wilson could be a tall order for Baker Mayfield, but he may just have the tools to do it.