First off let me say that although they aren't by any means perfect, zones aren't as broken as you think. Basically, yellow zones aim to keep everything in your zone in front of you. In Madden, it is a little extreme as players in yellow zones basically don't react until the ball is caught.
The slider you'll need to bump up is pass rush ( I have it around 75), and pass reaction time; I'd put it somewhere around 60, then raise/lower it depending upon your own skill. What you want to have happen is to get just enough pressure with your front 4 so that the receivers cant get deep and break apart the zone, but instead the QB has to settle for a throw to the flats. Upping pass rush should help your zone blitz succeed too, especially if you hit the weak blocking side of the formation.
Remember, pass rush is almost non-existent on default Madden settings. And you know what happens in the NFL when a team can't get a pass rush; basically every QB can have high comp % against a zone, and elite QB's will absolutely destroy it.