First off I am 140lbs and 5"4' . I ordered a Medium. I got this after having my baby almost 2 years ago and I couldn't bust these last few lbs.
The tank works great, its double layered and really does smooth and doesnt ride up at all.  In fact it rides pretty low (im 64 inches) and hits right above the bum.
 However it shrinks your chest as well...something that was NOT planned.  Im a shy 34B and it really disadvantages smaller chests.  I supposed if you wear a padded push up, you can make up for it but it will just make it feel a little tighter.  I also went for a walk around my neighborhood and was so HOT... so don't layer up on this.  I still wear it with tigher sweaters and unforgiving materials but I just sub in a push up.