Red zone scoring % is one of those metrics that just grates, every damn time. Did you kick a field goal or score a touchdown? doesn't matter, counts the same to this silly metric. Did you go for it on 4th down and pin your opponent on the goal line? kind of different than missing a field goal attempt or throwing a pick. What about hitting a skinny post from the 21? doesn't count. If the metric demands an arbitrary line, the 20 is a bad arbitrary line to choose. If the metric demands binary descriptors to nonbinary outcomes, it's a bad metric.
At very LEAST use something like points per scoring opportunity (trip inside the 40).