​Fast food restaurants should start selling 1/5 pounder burgers for a higher price than 1/4 pounders.

Think of it as shrinkflation in plain sight. The general populace will think 1/5 pounders are more meat because 5 is bigger than 4, and will believe the price increase is justified. At the same time, the difference is so subtle and can vary so much that most people won’t notice the difference anyway, but due to mental priming, they’ll believe they’re getting more burger.