Alexis
when grounding & un-grounding the antenna changes vswr it indicates you have common mode current flowing on that wire & radiating, either when its connected or when its disconnected,
my money would be on you have increased cmc on the wire when you connect it because 20ft is closer to an electrical 1/2wave than it is odd 1/4wave multiples (3/4wave)
if it was closer to 3/4wave i would have said the opposite, disconnecting it from the ground rod would cause an increase in cmc,
electrical 1/2waves of any conductor such as the mast, outside surface of coax braid & ground wires that are connected to ground at one end & the antenna radial coax junction at the upper end, have a low common mode impedance,
that promotes high current & unwanted radiation,
most of the difference people see in signal when comparing vertical antennas at the same tip height is due to this unwanted radiation not the antenna istself.
when you can't adjust vswr very low by pulling the gamma rod & radiator length you have to adjust the gamma strap/dogbone up or down a little & readjust the other two again.
good luck,
