Any if there are 4 seats at a particular price, you take them, the price will go up to the next fare class available - not down. So your theory doesn't apply.
Wrong. That is exactly what happened to me last year with a market leading loco airline.
Only 7 seats left at this price (£22.49). Seven days later, only 7 seats left at this price (£15.49). So the price can actually come down.