Hi Astrology
The principle of Jupiter is expansive, it enlarges ones ability to 'see' and intuitively understand as well as exercise efforts to enlarge one's experience in the areas (house, sign) that surround or are affected of Jupiter's traits.
The script of Sagittarius (higher knowledge, wisdom, a verve to experience freedom in the research of those things hidden, occult knowledge, interests in foreign espionage affairs which may or may not be connected to law (Sag. of the 9th house is in a hidden 12th house position to the house of law or judgement 10th), you could serve as research assistant to uncover ther finer statutes that involve research of many different types of study. It is not slight to make an easy description of the expansive quality of Jupiter in the 12th house.
Jupiter in the 12th house deals with foreign affairs, you may experience trials of learning experiences of physical sports venue, or you might find yourself expending more of your case outflow on gaming than having gain come your way in betting arenas in your life.
The natural houses of Sag. & Pisces certainly come into play and have much to do with the way you will experience the energies of Jupiter (dignified) in his own house and sign.
The control factor should be considered those things or areas in your life which you bring upon yourself. You have the ability to 'intuitively' know about the next ditch in the road ahead, that is, if you train yourself to be aware of you 'subconscious voice' warning you ahead of time. Jupiter in the 12th house sometimes makes for an effort of disengaging oneself (freedom at any cost) from dogma of one set example. Many irons in the fire in the pursuit of a perfect religion may find you facilitating in beliefs which will make for disillusioned karmic feelings, emotions creating depression.
The Father image is important, the expectations of the parental figure often are not met which causes the self to delve deeply into inner escapism, the individual finding refuge in his idealisms of just how one should view his Father in heaven, or the higher self. Consider the aspects of planets stemming form each house for these energies to appear. So you see it is not an easy effort to know how the great benefic will enlighten one (a better-best trait of Jupiter) within this house for it is 'deep' dark, and can be felt as an epiphany of wisdom of ones self at times.
Take care of the Square energy (depression) you might feel-Jupiter makes a square (obstacle related to the houses he is effective of) with Saturn within the 3rd H.C. (daily thinking patterns, siblings etc), the third house is considered the lower area of thought rather than the higher expression of 9th house realm.
Just a few undercurrents of some great good of Jup. the great ego, benefic.
Sincerely
Student of Astrology