Ideally that's fine... But in the end only thing is about clearing WL/RAC passengers (fully automated) and
not much about the ground situations !! I've myself expected an upgradation while travelling in the SBC MYS Sector in 3A, to 2A/1A but it never upgraded. Later got to know lower class needs to be booked fully!!(In SL too, daily pax fill it up but bookings are empty)
Higher classes going empty as such, isn't IRs "concern".