Well, it makes more sense when it's about values, so I'll just go make up my own theory if it's not about values. I mean, I thought the whole basis of calling types rational or irrational was that the rational ones had leading functions that involved making judgments, thinking being about
epistemic judgments and feeling about
situational judgments (see here:
http://wals.info/chapter/76), which are also called facts and values. If it's literally just about thinking or feeling we may as well go do MBTI and talk about how cold and unfeeling we all are since we're INTJ Masterminds. I could have sworn I've seen some authors make it about facts/values even if not all do though.