DAVIE, Fla. (AP) -- Ryan Tannehill stood in the Miami Dolphins' practice bubble Tuesday lobbing a succession of 35-yard passes, hitting each receiver in stride and making it look easy.

It's not.

A controlled-climate atmosphere with no pass rush, no secondary and receivers running at half speed isn't quite the same as going deep in New England in December. So we won't know for a while whether Tannehill has improved his accuracy on long passes, a glaring weakness in his first three NFL seasons.

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But two weeks into training camp, Tannehill senses progress.

"Not only am I better at it, but our receivers are doing a great job of adjusting to the football and making plays on it when it's in the air," he said. "I'm excited about that and the potential that we have. It's something that's going to be a factor for us."

To support his contention, Tannehill's success rate on deep throws in practice has been higher than in past years. He caused a stir Sunday with three long completions during team drills.

A breakthrough? Nah, veteran receiver Greg Jennings said.

"You can't put so much into it," Jennings said. "I'd love to say we're going to complete deep balls this year at a high percentage. But none of this now means anything if we can't translate it into games."

While Tannehill has steadily improved overall since he became a starter as a rookie in 2012, his grade on throwing long remains incomplete.

Last year he connected on 24 percent of his passes thrown more than 20 yards (10 for 41), which was even worse than his career figure of 27 percent. Aaron Rodgers, by comparison, hit 51 percent last year (20 for 39).

In 2014, Tannehill threw one touchdown pass that traveled more than 20 yards in the air. Andrew Luck threw 11 and Rodgers nine. Peyton Manning, Joe Flacco, Ben Roethlisberger and Tony Romo threw eight each.

During the past two years, Tannehill frequently misfired when speedy Mike Wallace was open deep. They were never in sync, and Wallace was traded to the Minnesota Vikings as the Dolphins revamped their receiving corps this offseason.

The wideouts this year are expected to be newcomers Jennings and Kenny Stills, top draft pick DeVante Parker and Jarvis Landry. But because of injuries, Stills (calf) and Parker (foot) have yet to take the field in training camp.

"They're two guys that you expect to be a big part of our offense," Tannehill said. "To not have them out here, it definitely hurts. Somebody is going to have to step up."

The Dolphins also need someone to step up at guard, the biggest question mark on a perennially unsettled offensive line. Tannehill has been sacked an NFL-high 139 times in the past three seasons, and shaky protection makes long passes tough to get off, much less complete.

"To be able to throw the ball down the field, you've got to have time," coach Joe Philbin said. "You've got to be able to set your feet and follow through to have a chance to complete those passes."

When given time, Tannehill has showed this summer he can complete the deep pass, Philbin said.

"He's throwing ball better this camp than he ever has overall," Philbin said.

Tannehill has yet to lead the Dolphins to a winning season, but last year he became the first Miami quarterback since Dan Marino to throw for 4,000 yards. Improvement on deep throws would boost that stat, as well as the team's winning percentage.

"He has taken a lot of heat over his first three years," center Mike Pouncey said. "But he just kept getting better, and we're looking forward to him leading us to where we want to be this year."