I have experimented with all shapes for the mist producing chamber. The piezo is the main component with diameter of 1.5cm. The height of the element is ~1mm.
I thought of two ideas for the chamber. The first is like a standard room humidifier design with a cylindrical spring loaded latch.
The second design in a strap on piezo cap on horizontally oriented wick container. The strap are press fit on the cylindrical surface.
Among the two pics first is horizontal orientation while the later is vertical.