She was very explicit about some things....it was a split, it was a small flight...probably 4 steps to the bathroom/bedroom level...and the bathroom was across from the bedroom.
The house had to be one of the people Ford mentioned unless they broke into a house....raided it...used their pool...etc etc.
NONE of my splits had a small flight to the bedroom level....that was the full flight. And none of my houses had a bathroom right across from a bedroom.
You are assuming something happened to Ford. She created the imaginary house and populated it with real people.
Except she said they “ping-ponged” down the stairs. That to me suggests a long narrow stairway.
Ford conveniently cannot remember who the sixth person, another boy, was at eh party. He was probably the home owner unless they broke into someone’s house.... even if such a “party” actually happened.
The house Wheland posted as Garrett’s was a two story, not a split level.