What happens, is each time you use an ice spell, you freeze them, right? Take ice blitz for example. Each freeze is worth 15 seconds, but the time doesn't stack. For example; if you cast it 4 times, you still only freeze them for 15 seconds, and they are imune to every 5th freeze or so. But, if you cast ice, blood, blood, ice, blood, blood, ice, blood, blood ice, their frozen for the same amount of time as ice-ice-ice-ice-ice. Ice hits 2 more than the closest barrage spell.