a more practical issue is where would Iran jump off with Israel?
Iran does not share a border with Israel, Israel only have border with Lebanon, Syria Egypt and Jordan, and Iran have either Turkey or Iraq to go thru before they can reach Syria, i seriously doubt Turkey will let Iran transit thru their territories, and Iraq is littered with US forces there, any movement there will alert Israel before even their force left Iran. And I doubt even Iraq government would allow Iran to transit thru their territories to get to Syria or Lebanon
The other way they can go is go all the way up Red Sea into the Med, which was controlled by NATO, it's going to take them ages and not guarantee they aren't going to be blockaded before entering the med. There are no practical way for them to heavily involved, other than firing missile from their off.
Any war between Iran and Israel has to be a ground war because Israel have unparallel advantage on their Air Force (Seriously we are talking about latest version of F-15E, F-16 and F-35 against Migs F-14 and F-5) and you are talking about launching strike into Israel with these legacy platforms, that's more or less suicidal, and you have to have way to deliver your troop and armour to the battlefield if you want to be a part of it, and I don't see how Iran can do it unless either Turkey or Iraq open their border for them to f with Israel, I just don't see how this would happen.