From the top. Tuberous aroids usually have a amooth, rounded bottom and a rough top, with the undeveloped growth a sharp cone. They only root from the top.
Soil mix isn't very important for this plant. Plant it, water well then wait to water again until it emerges.
Keep in mind it is a spider mite magnet. Spray the whole plant with water once a week to help prevent them.
__________________ May the bridges I've burned light my way.