When I put two vertically stacked spaces into one thermal zone in OpenStudio. The simulation results shows that the floor area is just half of the total floor area. Even though I have checked the "Part of Total Floor Area" in OpenStudio for each space. Looks like the internal gains (people, lights, electric equipments) were defined as per floor area, so I assume in EnergyPlus simulation they are also reduced by half. Is that what's expected?