Is your fighter a War or Theatrics? DFA and Feint have very different attribute requirements, DFA requires Strength, Stamina and Size while Feint uses Intel and Agility.
Feint can also activate nearly every 1 or 2 rounds, DFA is about every 3 to 4 rounds when working well. Are your fights going at least 3 or 4 rounds or do they end very quickly which may be the reason you are not seeing DFA activate if his required skills are not very high.
Do your fighters attributes coincide with the requirements for the skills? Also Intelligence plays a roll in how often activated skills will go off. A not so smart fighter will not use all his skills very much.