That would depend on the surface of the ice. Many might think the surface may be smooth and flat. That isn't always the case. It may have pressure ridges that rise several feet. Not sure how well they could discern the surface condition, as time of day, angle of attack, etc, would affect their ability to make that judgement. Not to mention being occupied with getting their exposure suits on.

They may have determined they knew what the sea state was and went with the "known" quantity. Also, I'm sure the ice looked very small to them. Would be interesting to see a comprehensive debrief of the pilots.