The Eagles' defensive line was incomplete for the last two months while Fletcher Cox took advantage of the "voluntary" part of voluntary workouts. But Cox is back in Philadelphia this week for the team's mandatory minicamp that begins Tuesday, and his presence changes the outlook at the position.

Cox will join Bennie Logan in the middle of the Eagles defense. Logan, a third-round pick in 2013, has started at nose tackle for the last three seasons. The Eagles' scheme change will have a major effect on Logan, who must transition from occupying blockers while lining up over the center to turning into a penetrating tackle.

"All those guys have an adjustment period," defensive coordinator Jim Schwartz said. "It's not just a change of position from a nose to a defensive tackle. It's really a change of philosophy from an at-the-line, two-gap philosophy to an attack, get off the ball, and one-gap penetrate philosophy. So those guys have had some ups and some downs."

Logan does not want to be a labeled as strictly a nose tackle. He played as a defensive tackle in a 4-3 scheme at LSU, and he said his responsibilities are "a lot similar" to what he did then. In fact, when the Eagles drafted Logan, there were questions about whether he was big enough to man the middle of the line in a 3-4 scheme.

Through his first three years in the league, Logan has mostly been a run stuffer. He has only three career sacks. Logan came off the field in many passing situations, but that was not considered a strength of his game or a key part of his responsibilities. In the new defense, he will be more involved in the pass rush.

That's why Logan has adjusted his body for the scheme. He dropped from about 315 pounds to roughly 305, which he thinks will allow him to rush downfield.

"It helps me get off the field quicker, helps me move better, and takes a lot of pressure off the body," Logan said.

The Eagles need depth at defensive tackle, and they failed to address it in the draft even though that position was lauded as a strength. Howie Roseman, the executive vice president of football operations, thought the Eagles would be able to select one, but the team lacked second- and fourth-round picks.

They added undrafted linemen who coach Doug Pederson said have "really shown flashes of giving us depth at that position." They return Taylor Hart and Beau Allen from last year's team. But a key name to watch is a veteran Mike Martin, a 25-year-old the Eagles added in April.

Martin, who played four years with the Tennessee Titans, registered four sacks combined in 2012 and 2013 while playing in a 4-3 defense. He was held without a sack in a 3-4 defense for the last two years, and he thinks he can benefit by coming to this scheme. He was a beneficiary of Cox's absence, filling in with the first-team defense often during organized team activities.

"You can't take it for granted," Martin said. "It's big time, getting reps."

But the strength at the position will clearly be Cox and Logan. The two are close, playing next to each other for three years. Logan wasn't worried about Cox missing time, saying that "once he learns the plays and what he's got to do, communication will be the same."

Depending on their contract situations, Cox and Logan could become fixtures in the middle of the Eagles' defense. Cox's contract expires at the end of the year - that was the reason for his absence - and Logan is also entering the final year of his deal. His numbers could improve playing next to Cox and in this defense, and although he won't get the fanfare of Cox, he is similarly a key part of the Eagles' defensive line.

"Every year is a contract year to me," Logan said. "I never approach this as going in the fourth year of my contract. While I'm here, I'm going to be here, I'm going to have fun and enjoy the moment. And when the contract stuff comes up, we'll talk about it. But right now, my focus is the upcoming season."

zberman@phillynews.com

@ZBerm