I may be completely missing something, but I was under the impression that floating ice has zero impact on sea levels - a unique characteristic of water. Ice fl

I may be completely missing something, but I was under the impression that floating ice has zero impact on sea levels - a unique characteristic of water. Ice floating in water in a cup already at the top won’t overflow when it melts. It seems like only land-supported ice sheets would have any impact at all anyway. Where were they getting the 6 foot rise in the first place? The violent water displacement when the cliff falls?