In floor mode, air will still flow out of the 2 outer vents in the dash. Biggest problem is the drivers side air floor to the floor is reduced, which causes the interior to get hot (over temp) because there's not enough air floor to the floor. So the interior air temp sensor, which is located down by the drivers right knee (small grill in lower dash) doesn't sense enough warm air flow off the floor because half the air flow is routed to the dash left vent. Best fix is to just close the left dash vent in the winter, which will force all the "floor" air to the left floor and satisfy the temp sensor sooner.
There was a big long topic on this about 3 years ago. I really think Toyota miss designed the heater/AC ductwork, because there is hardly ANY air flow out of the 2 side window vents located on the TOP of the dash, so the "floor" setting was changed to always have airflow out of the 2 outer dash vents in "floor" mode.
