Stealth hiding above a doorframe

Furber shoved the letch out of the way and peered into the cell. It was a gray concrete room with a steel cot, a steel toilet, and a pair of fluorescent tubes ten feet up behind a wire cage bolted to the ceiling. The tubes washed out everything in the cell and made it look pale.
It was empty.
The cot was placed to make hiding beneath it impossible, and the sheets were still wrapped around the thin mattress without a wrinkle on them. The toilet wasn’t large enough to hide behind and was bolted in the corner, anyway. The cell wasn’t much wider than the door, but he craned his neck to make sure no one was pressed into the small space on either side.
…
The lieutenant inched the door open. It rolled back into the frame until it hit the full-open position with a thud. He mouthed a three-count and he and Jake swung into the tiny room.
Nothing.
He gestured for Jake to cover him and crouched by the cot. The flashlight beam swept back and forth beneath the steel frame, highlighting areas he could already see by the light of the tubes.
“Shit,” Furber said again. He turned to the men in the hall to have them call in an escape and saw her over Jake’s shoulder.
The woman in black was upside-down in the three-foot space above the door. Her back was pressed against the wall and her feet braced against the ceiling. She balanced on the half-inch door frame on her fingertips.

Excerpt From Ex-Patriots, pg 448, 450
Peter Clines
https://books.apple.com/us/book/ex-patriots/id585738393