Roger, unless I’m mistaken the EX-3 will have a zebra option (it’s a viewfinder display) that can be turned on and off. Most pro cameras have this and will let you set it to a variety of levels. My JVC HM-750 lets me change mine from 70% to 100%. I have it set to 70%. I adjust my iris so that the zebras start showing on a person’s face and then go up another 1/2 stop. Every camera will be different so you’ll need to do some test shooting and see how yours acts under different situations.
BTW, unless I have no choice (for example, run and gun situation) I always shoot in manual iris mode.