What is the problem with smacking them close in? Better than not at all, surely.
First, if it’s an IRBM or ICBM with a nuke warhead, you absolutely must intercept it above the atmosphere, preferably hundreds to thousands of miles away from your country’s borders. Also, the Iron Dome type of system is simply not designed to take out the much larger sized missiles that would be launched from Iran. Iron Dome does not pack the weight/payload that would be sure to take out an ICBM, even if it could hit it. Could Iron Dome score hits as a last gasp effort against ICBMs that otherwise would get through? I don’t know but I have never seen reference to that kind of testing for Iron Dome.