The Wavelan icon cannot be resized.
If you turn off "Adjust icon automatically", changing the panel icon size will not change the Wavelan icon size. All other xfce4 panel icons change, Wavelan stubbornly stands in its oversize.
Current XFCE4 4.18.0 icon theme is elementay, current Wavelan icon is fixed size from Adwaita.
Wavelan 0.6.3