Reason No. 206 to be discouraged about the Dolphins: Even the areas they assure us will be strengths never quite seem to measure up to expectations, and we’re seeing that play out yet again.

The Dolphins presumed they would be very good against the run and generate a bunch of explosive plays and even told us to expect more impact plays from their new linebackers and that Ryan Tannehill would make the greatest jump of the second-year quarterbacks.

Now consider reality:

### Run defense: For all of the hype around the front seven, any suggestion the Dolphins are among the best against the run is pure myth. They were at one point: In 2011, their last year in a 3-4 defense, they ranked third. That slipped to 13th in 2012, and now they’re 19th.

And despite the depth on the defensive line, this unit often wilts against the run late in games. Miami is allowing a deplorable 5.6 yards per carry in the fourth quarter, more than any team permits over an entire game. The Bills churned out 10 yards on a key run to make their game-winning field goal closer; the Patriots averaged 4.8 on the ground in Sunday’s fourth quarter.

Paul Soliai and Randy Starks are grading out very well, but Pro Football Focus ranks multiple other players in the bottom half-to-third of defenders at their position against the run: Cameron Wake, Olivier Vernon, Dannell Ellerbe, Philip Wheeler, Chris Clemons.

And incidentally, this defense is clearly worse since Joe Philbin and coordinator Kevin Coyle arrived and switched them to a 4-3. In 2011, this unit ranked sixth and allowed 17 points per game. This defense is 20th and permitting 23.9.

### More explosive plays: Another unfulfilled promise, and a big reason why the Dolphins rank ahead only dreadful Jacksonville in AFC total offense.

The Dolphins have managed only 25 plays of 20 yards or more, tied with Cleveland and Buffalo for 23rd in the NFL. That’s 3.5 per game, barely ahead of the Dolphins’ 3.4 per game in 2012. The Jets, by contrast, have 31, despite Miami possessing superior skill position players.

Mike Wallace, billed as one of the top deep threats in the game, is tied with Jeremy Kerley and Ace Sanders, among others, for an absurd 70th with just four plays of 20 yards or more. That’s behind 69 other players, including the likes of Doug Baldwin (8), Ted Ginn and Jason Avant (6). By contrast, Baltimore’s Torrey Smith has 14.

Wallace remains frustrated and had another conversation with offensive coordinator Mike Sherman about it in recent days.

“We’ve got to be able to throw the ball deep,” said Wallace, whose seven drops are third most in the league. “We have to be able to back people up and not have people sitting us. We have to balance it out.”

Sherman said he has tried to throw deep, but “for whatever reason, something has happened here or there.”