What will always work is balancing your heavier top half with your smaller bottom half to create the illusion of a proportionate figure.  A tube top will be revealing too much skin and accentuate your  problem area. Try a top with a deep v-neckline instead to look leaner on top. Match them with an A-line or pleated skirt to create a fuller bottom. If you really want to wear a tube top, go for a drop-waist tube dress that skims rather than cling to your body.