Food for thought, although I have not ever actually used this feature yet, but what about doing the AP TAG feature under Access-Control ?
So tag 4FL for 4th floor access points, and 3FL for 3rd floor access points, and then under access control, change VLAN ID and click 'add vlan' and insert the tags and insert the VLAN.
I feel like having never actually used that feature, but from what I'm seeing on the settings, that it would do exactly what you want.