The phrase "assembled behind" is correct and usable in written English.
It can be used to describe a group of people or objects that have been gathered or positioned at the back of a particular location or formation.
Example: "The team was assembled behind the stage, ready to make their entrance."
Alternatives: "gathered at the back" or "positioned behind".
Meanwhile, rivals assembled behind Sun Microsystems as it tried to lift Microsoft's iron grip on software.
Russian fans who were assembled behind the goal threw flares onto the field not long after the match started.
It was reassuring to see fresh ingredients being cooked rather than processed components being assembled behind the scenes, McDonald's-style.
With just about 70 days left before the inauguration, Mr. Trump's administration is largely being assembled behind the scenes.
Nobody's going to come even close to beating me in 2020," Trump said, as the sheriffs assembled behind him burst into applause.
At 3 55, dozens of officers in riot gear assembled behind the stage, at West 118th Street and the section of Lenox Avenue known as Malcolm X Boulevard.
Decisions were made at annual or semiannual meetings in Amritsar, when groups would assemble behind their elected leaders in the open area in front of the Akal Takht.
The chat show host headed into the audience during the ceremony and whipped out her smartphone, passing it to Cooper and beckoning pretty much the entire front row to assemble behind her.
The 82nd Academy Awards are not beginning just yet, perhaps because the guests are still assembling behind closed doors, fighting over their seats and firing air kisses across the aisle.
The 2nd Corps re-assembled behind the Prijedor OG 10 and Serbian troops.
Finally then, two days before the start of Operation Commando, the 28th Brigade crossed the Imjin river to assemble behind the 25th Brigade on 1 October.
