tai chi is all about balance, offense and defense contained in one, separation within the connections... connections within the separations. terms like 'combat tai chi' don't sound right to you only because of your perceptions, not reality. time to change the paradigm.
think, if you were only reacting defensively to attacks your yin would exceed your yang. now, expand the paradigm, and think in terms of RESPONSE rather than REACT. now you have the potential for a more balanced approach, responding to a CATALYST be it threat or a signal, instead of waiting for an attack to react against. that is too late, too slow.
the trick here is to avoid ANTICIPATING, and that is where partner drills and pushing hands begin and sparring needs to be involved, so that you can use the present tense meditation practices from your Qigongs and form practice and apply in fighting, altercation, combat whatever you want to call it.
develop the physical and psychic sensitivites to the point where you can dispatch your skill when needed, as a response, containing both offense and defense together, in balance.
pete