Kristaps Porzingis puts up a shot during the first half...

Kristaps Porzingis puts up a shot during the first half against the Washington Wizards at Madison Square Garden on Thursday, Jan. 19, 2017 Credit: Jim McIsaac

DALLAS — Kristaps Porzingis and Jeff Hornacek sat together under a basket and had a private film session. Hornacek’s laptop was open and he was showing Porzingis video of his shot, trying to help the Knicks’ second-year big man recapture his rhythm and form.

Porzingis missed his first six shots and had two turnovers before making his first basket in Monday’s win over the Pacers. Porzingis finished 3-for-13 with eight points.

He said the poor shooting night has nothing to do with the left Achilles issue that kept him out of four games recently. Porzingis also dismissed the idea that having a big bump on his shooting elbow — he said it’s swollen from a fall “a while ago” and he doesn’t “really feel it” — has affected his shot.

It’s all mechanics.

Hornacek, a great shooter as a player, could be seen raising his right hand over his head and simulating shooting during their meeting on the Mavericks practice court Tuesday. Porzingis was all eyes and ears because he’s been frustrated with his play. He watched video on his own, trying to discover what the problem is, before sitting down with his coach.

“I watched right after the game, and now he just wanted to go over my shot again,” Porzingis said. “I had open looks. It’s just sometimes when I have that much space my shot is flat. When I have a defender running at me, that’s when I get it up. And that’s when it goes in.”

That was Hornacek’s advice to Porzingis: he needs to have his arm up a little higher because his shot can be too flat. Porzingis also noticed that he rushed his shot against Indiana a couple of times, or wasn’t as fluid when he got the ball.

“I know when I miss a lot of shots, I make it in two motions,” he said. “I go up, and I hold it up here, and then I shoot from here. But when I’m making shots, I just do it in one motion, I come and shoot it. I kind of saw it on film again.”

It’s been a rough stretch for the 7-3 forward from Latvia, who looks forward to facing one of his idols Dirk Nowitzki Wednesday when the Knicks play the Mavericks.

In his last five games Porzingis has shot 3-for-22 from three-point range and 22-for-58 overall. Two of those games were right before his Achilles flared up and forced him to sit out. Since returning three games ago, Porzingis is averaging 12.3 points and 3.3 rebounds. But he won’t blame the Achilles.

“It’s not bothering me at all,” he said. “I have to be smart about the way I warm up. I don’t want to get that pinch again so just really step by step every time.”

There’s no doubt Porzingis’ production has dipped since returning from his initial three-game absence because of the Achilles.

During a nine-game stretch from Dec. 11 to Dec. 30, Porzingis scored 21 or more seven times. Since then he’s scored 20 or more once in the seven January games he’s played, and he’s been held under 10 three times, including Monday.

“I think he’s fine,” Hornacek said of the Achilles. “I don’t think he has any problems with it now.”

Some of the dip could be attributed to Porzingis not getting the ball as much, particularly as Derrick Rose’s shot attempts have risen.

The Knicks were looking for Porzingis against Indiana, and he couldn’t convert. But Porzingis averaged 16.6 shot attempts during that strong nine-game span. He’s attempted 11.9 shots in his last seven games.

But Porzingis is focused on Dallas and playing against Nowitzki.

The Mavericks’ legend was sidelined when they met in November and Porzingis scored 24. He also hit Nowitzki’s patented one-legged step-back shot and stared at him. Nowitzki called Porzingis “cold blooded.”

“It was so random,” Porzingis said. “I didn’t even think about that move. It just kind of happened. I didn’t want to look at him. But for that moment I checked if he was looking at me, and I looked at him. It was fun.”

Kristaps Porzingis has struggled in his last five games:

PPG 10.6

FG % 37.9

3FG % 13.6