thanks for the "capacitance hat" search term. from googling it looks like this hat is electrically connected to the antenna? In my case if the "cap" touches the copper wire of the antenna - signal strength decreased. Only when I kept the cap close but not touching the antenna it performed well.
Sure, but that does not stop it from capacitively coupling it.
Even tape or insulation from a wire can, be used to electrically lengthen or fine tune an antenna. But thats less about capacitance and more about the electrical lenght being longer in the dielectric.
