My gut reaction is that signs where a planet is weak will increase its wickedness. The Sun in Libra or Aquarius could do damage to Venus if only because Venus through reception would be completely open to whatever detrimented nature the Sun would express through its application and combustion, just as the Sun in Leo is open and interested in whatever debility Saturn in Leo will express. Even gentle benefics Venus or Jupiter can play the role of a malefic if say they were 8H ruler Rx and peregrine applying opposite to and being received by a sig.