When Isaiah Hartenstein signed with the Knicks last offseason, the center came advertised as a strong facilitator who could space the floor, shoot the 3 and defend the rim.

Halfway through the season, Hartenstein has been a solid defensive presence but offensively has lacked a finishing touch inside and has not been asked to be the kind of distributor he was last year in his breakout season with the Clippers.

“It’s been up and down,” Hartenstein, who had a lingering achilles issue earlier in the season, said Tuesday of his first half with the Knicks. “Some stuff is out of my control, some stuff is in my control. There’s been good parts and bad parts, but at the end of the day, we’re doing good as a team. That’s the most important part.

“There’s stuff I can definitely do better than what I’m doing right now and that’s on me.”

Hartenstein has played in all 41 games this season and on Monday night got the nod over Jericho Sims to remain in the rotation as the backup center with Obi Toppin returning from injury as the backup 4.

But the loss to the Bucks proved to be one of the more frustrating games of Hartenstein’s season. He brought down four rebounds (all of them offensive), committed three fouls and went scoreless in 10 minutes after shooting 0-for-6 from the field. That included a single possession late in the third quarter in which he missed three straight shots from inside the restricted area.

“Those are things that I can control and that’s what makes me confident that I know I can do it better later on, or the next game,” Hartenstein said after practice as the Knicks prepared to play the Pacers. “That’s a quick fix. It’s not like something where I’m doing complicated things like fadeaways, step-backs or things I don’t normally do. That’s stuff I know I can do. I’ve done it in the past, so I’m not really worried about that.”

It didn’t help that the sequence came during a 10-0 Bucks run that helped them get back in the game and erase a 17-point deficit. But it has been something of a growing trend for Hartenstein this season.

Entering Tuesday, 234 players had attempted 50 or more field goals from within the restricted area. Hartenstein ranked 219th in field-goal percentage at 54.1 (53-for-98). Among 63 centers in that group, Hartenstein ranked last. First in that category was Sims, who was shooting 84.7 percent (50-for-59) in the restricted area.

Last season, Hartenstein shot 72.8 percent from within the restricted area.

Conversely, opponents are shooting only 61 percent in the restricted area with Hartenstein defending them, which was the sixth-best mark among all centers with at least 300 field goals attempted against them.

“The rim protection is really good,” coach Tom Thibodeau said in assessing Harteinstein’s performance. “Obviously having the ability to play away from the basket opens up the floor for us. Puts pressure on the rim, the offensive rebounding has been really good. Play to your strengths.”

Except the Knicks have not used Hartenstein in the same role he thrived in last season, when he was a sharp facilitator averaging 2.4 assists per game. This season, he is averaging 0.8 assists per game and has been used more for his spacing.

“It’s been a little difficult, but at the end of the day, it’s about what the team needs,” Hartenstein said of adjusting roles. “Everyone sacrifices certain aspects of their game. Not everyone’s playing exactly how they want to play, but that’s every team. … Now I just kind of have to sacrifice one of my best attributes. But whatever the team needs. We got three guys that are very ball-dominant and I think that’s kind of how we’ve been winning. It’s hard to say much if we’re winning.”