The tunnel that leads from the home dugout at Coca-Cola Park into the IronPigs clubhouse provides a constant reminder of the mere 69 miles that separate the Phillies' triple-A players from the majors.

Play Like A Phillie Today is etched in white lettering, and the minor-leaguers walk past it every time they play in Allentown. It is both a tease and a goal, especially for the current batch of IronPigs, the youngest lineup in the International League and one expected to deliver pieces for the next competitive Phillies team.

The first month generated positives and negatives, and one prevailing theme: Discipline is a difficult thing for many of the free-swinging triple-A prospects. It's why the mantra "controlling the strike zone" has endured as a buzz phrase within the Phillies organization.

Five of the prospects - Dylan Cozens, Roman Quinn, Nick Williams, Jorge Alfaro, and J.P. Crawford - have struck out at a rate higher than the league average. Alfaro, Williams, and Jesmuel Valentin have walked at a rate lower than the league average.

Player development in baseball rarely takes a linear path. It's why the Phillies will exert patience when promoting their hitting prospects.

"You have to remember: Players in the minor leagues, when you get so close to the big leagues, they want to impress people," Phillies hitting coach Matt Stairs said. "How do you impress people? By swinging a lot. Maybe doing too much. Speeding the game up."

That is how first baseman Rhys Hoskins separated himself in the first fifth of the minor-league season. The prodigious power he displayed in 2016 at double-A Reading has translated to a higher level. He has reduced his strikeout rate and maintained his walk rate. The 24-year-old former fifth-round pick could tempt the Phillies later this month if the production continues.

"He does a lot of the things we want to see," Phillies general manager Matt Klentak said. "But he is a month into his triple-A career and we are happy to let him get at-bats there."

In reality, the Phillies cannot and do not expect polished products to graduate to the majors. Alfaro, Williams, Cozens, and Quinn have carried a reputation as free swingers throughout their minor-league careers. That does not diminish their potential; it just causes the Phillies to demand a little bit more before a promotion.

A functional lineup need not contain eight hitters with special walk rates and a disdain for strikeouts - especially not in the modern game that has placed a premium on power and shrugs on strikeouts.

But the Phillies have stressed a patient approach in the minors. Some younger players are more receptive than others. Swings may push a player to the majors, Stairs said, but it's what led to that swing that could be just as important.

"It's real difficult at times," triple-A manager Dusty Wathan said. "I think most of them realize it. The problem is you have to remind them all the time. They tend to wander, young guys. Right?

"So you might tell them one day. Then, all of a sudden, they go 2 for 3 or 1 for 3. 'Oh, man, another 3 for 3 and I'm out of here, guys.' Whoa, whoa. You have to remind them."

The strikeout and walk rates in the National League and International League are almost identical at 22 percent and 9 percent, respectively. But a minor-league player's combination of a high strikeout rate and low walk rate typically does not profile well for major-league success. The pitching is harder. The holes in a player's swing are more exploitable.

Wathan used Cozens as a recent example. He went 3 for 4 with a double and deep homer in the first game of a doubleheader at Toledo. They threw him fastballs. In the second game, with a more veteran catcher in the lineup for the opponent, Toledo attacked Cozens with breaking balls and fastballs out of the zone.

He went 0 for 5 with four strikeouts.

"I think it was a good learning process for him to realize it," Wathan said. "They knew he was going to swing and he wanted some hits."

So Wathan and his staff search for small adjustments. Cozens, in 23 plate appearances during his first six games of May, walked three times and stuck out just three times. He had six hits in 18 at-bats. Progress began with some better discipline of the strike zone.

"He realizes it," Wathan said. "He's working at it. It's just hard. You're so close here. You want to do so well. He tries to do too much at times. They all do. It's human nature."

It's why Alfaro, who struck out 26 times against one unintentional walk in his first 23 games this season, will have to improve his pitch recognition before returning to the majors for good. He may, ultimately, be a player who strikes out at a high rate but still provides value. For now, the Phillies will extend the development process.

Is it possible for a player to learn plate discipline?

"You can," Stairs said. "The older you get, the more you learn of the strike zone. The more you learn your strengths. You start sitting on different pitches more often. That's what you try to preach."

mgelb@philly.com

@MattGelb