Anne, the top is not voluminous, exactly, but it is definitely not fitted. Fluid fit. I did stay folded under just fine throughout the day. I had to adjust when I went to the bathroom. But otherwise it stayed more or less put without fuss.
I find this usually is the case. But it works most easily with tops that have a band or welt at the bottom, as this one does. That already reins in the volume to a degree. Plus, it's not super long. It hits at my hip if it's not folded under.
Still, I managed to do it with several linen tees and sweaters that are unbounded during the summer and it worked fine.