When glaciers get bigger/heavier they tend to go down hills more... That's what glaciers do...
Actually, as ice warms, it flows more. Think of molasses on a warm pan...it spreads out farther in a thinner layer than if it's cold.
Plus, as the glacier bed warms, there's less friction to hold the ice back from flowing, flowing on a thin water film.
Also, with Antarctica, as it reaches the sea, the ice floats up, lifting the ice away from the rock bed on land. As the waters around the land get warmer, that water can melt farther and farther inland under the glacier...i.e., even less friction, so more flow.
In other words, greater ice
extent is a sign of warming, depending on other factors.