My understanding is that imperfect contrition is because you ONLY have a fear of hell, but not the rest (for instance, being sorry for what you’ve done). Perfect is when you are contrite in the sense that you have hurt God, are sorry you have hurt someone else etc + the rest. Perfect contains imperfect in that sense, but it has been made perfect. Or you could phrase it better to say that Perfect is this, and imperfect is perfect minus this.
So if you are imperfect, you haven’t gotten perfect. If you are perfect, you are no longer imperfect. In that sense, you can’t be imperfect and perfect at the same time, it’s just not logically sound.