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0.6 is less than 1.8, so 0.6 would use thinner wire or less wraps to make the coil. So as there's less resistance, it requires more power.
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For the Same Alloy of Wire. A Thicker Wire has Less Resistance than a Thinner Wire.
Think about for a second...
Have you ever run a Power Tool using an el-Cheap-O 25 Foot Extension Cord that is about as big around as a Pencil? The tool Doesn't run very fast does it. And the Cord can get Warm.
But when your Neighbor, who is a Contractor, loans you his Extension Cord that is about as Big around as a Quarter the Tool Runs at Full Speed just like it was plugged into the wall. And the cord Doesn't get Warm.