Here is a mod to the Lotus stem bowl and the WPA bowl that works well for microdosing. It reduces the bowl size from 13 x 10 mm to 13 x 3 mm and uses our standard stem screens and debris screen. It also raises the screen above it's usual position and reduces 'dead' air above the herb.
Standard screen on bottom. Debris screen forced into bowl and flipped over so edge is down, standard screen on top of that.