IKE is a good measure for how serious the surge might be over a wide area since it takes into the account the entire area affected by strong winds, which is what moves more or less water. As IKE increases usually more water is being moved even if the max sustained winds might be decreasing. Larger storms move much more water, which then gets funneled into bays and harbors. Maybe Milton didn’t have time to take advantage of a larger size area of strong winds to build a surge but we’ll find out soon.