Nico Hulkenberg and Kevin Magnussen were disqualified on Saturday after post-session examinations of their cars showed their DRS wings opened more than the 85mm that is allowed in the rules.
Talking about how Haas had found itself in such a situation, team principal Ayao Komatsu said it mainly revolved around a lack of communication between the departments of his team about the implications of a new rear wing design.
A concept shift meant the rear wing elements sloped up near the endplate, something that needed to be taken into account when setting the maximum allowance for DRS opening.
However, the design department had not explicitly warned the track team about this matter, and testing by the squad in Monaco had not been thorough enough to check the gaps across the entire span.
"If the designers had made it absolutely clear that the design intention was slightly different from the wings you have been using before, so you have to check it in this way, that would have helped," said Komatsu.
"But at the same time, even with other information, the trackside checks should have checked the whole legality surface.
"There was no performance gained, absolutely zero, but that's not the point. The car has to be legal.
"We just have to accept this as a failure of the team, and then learn from it, and make sure we don't make the same mistake again."
Komatsu believes that the DRS exclusion was something that showed the team needed to improve its processes to prevent a repeat in the future.
He added: "For the designer who designed it, in his mind it's clear: 'this wing is legal, but it's got a different profile'. So he needed to think, 'should I communicate that to make sure that other people who didn't design the thing understand it?'
"For the trackside people, if they had had that highlighted, it would have helped. But even without that, with a brand-new rear wing, just don't assume anything. You just have to check every single legal surface: that's what we should be doing.
"So again, a bit of complacency, a bit of assumption, without actually thinking 'Okay, this is the new rear wing, it could be different.' We just need to improve working as a team."
With the wing issue being more about how the team set the maximum DRS opening, it has not needed a change of specification for the race, so the team avoids a pitlane start.
Asked what the team would be running in the race, Komatsu said: "It's the same wing, but we can adjust it.
"With the DRS open gap, there is a mechanism to adjust it for where you are going to get to the maximum.
"We have a parc ferme request to adjust it. So that is legal, and it's been approved. So, we adjust it on both cars and we start from P19 to P20."
