easyice,
Not a stupid question, I've had the same issue just this week. There are 2 workarounds that I have found.
First, the correct iris mode is just one (Next) mode away when you hold down the Iris encoder, so that gets you to the right place pretty quick.
Second, you may record a "home preset", then set that under "Show Settings" in the Setup menu. I have not tried this yet, but if you were to put all of your fixtures at the correct "home" position (with the Iris mode correct) then record this as a preset and set that preset in the menu, your Mac 2ks irises be open when they go home.
Hope that makes sense.
-Nick