Circulation ratio
The share of a home's carpet area given over to pure movement — corridors, passages, the floor you only walk across. The single most useful Subtract diagnostic: pure-movement floor ÷ carpet area.
Above 20%? Subtract here first
In an efficient compact home, circulation sits around 10–15%, mostly integrated. Above 20% and the plan is leaking space — circulation is your biggest Subtract opportunity. Below 12%, leave it and move to Layer.