It means if you were trying to get into Arstotzka wearing his face and a trenchcoat, you would need to stand on someone's shoulders who was exactly as heavy as you.
So you're saying, For janet to disguse herself as MrWillSauce, she needs to get his face, a trenchcoat, sit on someones shoulders and likely break 8 feet in height, while sitting on another person weighing 220 lbs and then be a 8-9 foot tall super skinny trenchcoat wearing monster with a 17 year old mans bleeding sawn off face strapped to her head. Into a booth that likely wont even fit her and her accomplice now.
I don't think it's quite as bad as you make it sound.
For one thing, the person on the bottom doesn't get his full height, he's missing the height from his head which overlaps the height of the person on top. Also, the person on top doesn't count any of their leg length. Effectively the bottom person loses 1/8 of their height, and the person on top loses 1/2 theirs. Assuming both are about 5' tall,
Bottom: 5 x 7/8 = 4.375
Top: 5 x 1/2 = 2.5
Total: 6.875
This would probably be taller than the original person, sure. But you can do a lot by having the bottom person hunch over and bend his legs, and the top person slide back a bit farther on his shoulders and also hunch over a bit. But if they straightened up they would look a bit like a looming stilt-walker.