Basic Positioning the Harp Wah: Like any new device, a bit of practice is necessary to master and maximize all of its effects. Here is how I hold this resonating harmonica "cup mute", which allows me to get great Wah sounds on the harp.
It may help to think of it this way…
Combine the technique of gripping a microphone (for amplified harp) with standard acoustic “hand-cupping” skills. Both of those techniques and principles apply here.
Like anything new, practice is necessary to master and exploit all of its potential.