while those refund tables are a nice idea they have absolutely no legal effect and are not binding on the passenger.

the correct refund for a downgrade would be the difference between the fare you paid and the lowest applicable fare (with same flexibility etc) in the lower cabin at the time you made the booking, or at the time of travel, which ever is the lowest.

An airline cannot charge for a service which is not delivered without fully returning any difference in cost.

Of course if the refund table benefits the passenger then they are free to accept it.