In Fletcher Cox, Vinny Curry and Brandon Graham, the Eagles have three players whose salary-cap hits for 2017 rank among those of the top 32 defensive linemen in the NFL. They used a first-round draft pick on Derek Barnett, and they traded down 25 spots in the third round to acquire Tim Jernigan. In short, the Eagles have invested a tremendous amount of their available capital in building their defensive line, and basic economics suggest that they will need to see something approaching a tremendous amount of production from the unit in order for the defense as a whole to reach its potential.

Last year, they got something less than that. The production wasn't awful. Not even subpar. It just wasn't what they needed, given the composition of the personnel behind them. If Howie Roseman was paying a cornerback $7.5 million this season instead of Curry, the roles might be reversed. But this defense was built with the thought that the front four would make the players behind it better. Significantly better.

If the Eagles are going to be better than what most of us assume, the pivotal variables are Carson Wentz and the defensive line. Thanks to the way the schedule falls, we're going to find out about that latter variable almost immediately.

In the Redskins and the Chiefs, the Eagles will open the season with two of the better offensive lines on their schedule. Washington, in particular, will offer an intriguing apples-to-apples look at where the front four stands compared with last season, when Jay Gruden's balanced offense spent the bulk of both games dictating the engagement. The Eagles will catch a break as All-World tackle Trent Williams serves a suspension, but the interior of the offensive line vs. Cox and Jernigan is where the game could very well be won.

You haven't heard the name Bennie Logan in the Eagles' locker room all that often this summer, mostly because the void left by his departure was presumed to have been filled — or even improved upon — by the acquisition of Jernigan, the two-gapper whom the Ravens traded rather than lose to free agency after the season. Logan's name is relevant, though, because of the stark preview of life without him that the Eagles got when he went down with a groin injury in a Week 6 loss to the Redskins last season.

By the end of the 27-20 loss, the Eagles had allowed a season-high 230 yards on the ground in a demoralizing loss, with Logan's absence the key. He was dominant in the 17 snaps he played, but the difference was clear when he was off the field, even before the injury. The Redskins' second touchdown drive began with Logan shoving Washington guard Shawn Luvauo to the ground and flattening Matt Jones for a 2-yard loss. Three plays later, with Logan and Cox off the field for a breather, Rob Kelley gashed a d-line anchored by Destiny Vaeao and Beau Allen for a 45-yard gain that set up a Vernon Davis touchdown catch. In the second half, with Logan out of the game for good with a groin injury, the Redskins ran the ball 14 times for 104 yards to close out a 27-20 win.

When the Eagles faced the Redskins again eight weeks later, Logan was back, and so, more or less, was the run defense, up until a 25-yard run by Chris Thompson with 1:54 remaining lifted Washington to a 27-22 victory.

"The couple times we played them last year, they were able to be balanced," Cox said. "We've got to make them one-dimensional."

The rumors of Cox's decline were a bit overblown. Logan's 3 1/2-game absence allowed opponents to key on his Pro Bowl teammate, and the lack of a consistent edge rush only hampered matters further. Still, the Eagles' salary-cap situation means they need production commensurate with salary from up and down the roster, and Cox's cap number will jump from $9.4 million to $17.9 million to $22 million between now and 2019.

"I was kind of behind last year from missing a lot of ball in the spring, and I was trying to catch up some," said Cox, who sat out the spring while negotiating his contract extension. "Things are going a lot smoother for me."

Cox can't do it alone. Graham has been an understated but impactful presence on the edge over the last couple of years, but the Eagles desperately need a source of pressure from the opposite side. Curry was paid to be that guy. Barnett has made a case to start over him. The identity of this Eagles defense will rest somewhere within.