You ground the HYBRID to earth and/or install a coax choke (10', 7 turns) right under the HYBRID. You can also increase the size of your coax cable and use 50' or RG-8X.

In addition to the earth ground and the coax choke I found that if I installed downward hanging (diagonal at ~45degrees) radials tuned to my frequencies of interest plus several (4-6) ground counterpoise I helped tremendously on reducing the common mode current. The ground counterpoise spread out the electrical RF ground area and the diagonal hanging tuned radials reduced the impedance of the HYBRID coax connection along with provided some radiation of my signal at their tuned frequencies (20, 15 and 10m).

Just some additional helpful info, 73. ...Joel N5JMP