Measure the cider reduction by final volume, not by thickness: stop when 3/4 cup has reduced to 1/4 cup, then cool it before adding it to the eggs.
Keep the muffin pan inside the oven when lowering the temperature from 425°F to 350°F; the temperature transition is part of the tall-muffin technique.
The cinnamon-sugar surface naturally becomes softer and slightly sticky as it sits, so the coating has its best texture relatively soon after baking.