7th lord Jupiter is in 12th house. Now, the main point is what a "house" is? A house is a zodiac sign which is a creation of human imagination by drawing imaginary lines between a few stars which appear to be lying close to each other on a plane surface in the sky. But the sky is not a plain surface and the stars are not fixed there side by side. But those stars are actually hundreds of light years ( a light year means the distance covered by moving at a speed of 1,86,000 miles per second for so many years or one light year distance = 584260 crore miles) away from each other both horizontally and vertically and have no relation, as such, between those stars. The distance of one star with another within the same zodiac sign is some 50 to 1000 light years between them. The zodiac sign, being an imaginary body does not have any homogenous existence and is not a body formed by nature. Therefore, the so-called effects of a planet being in a particular house is also based on imagination.
The next point is Jupiter is the lord of 7th house. Jupiter is a planet of Sun and has no power to go beyond the gravitational field of the Sun. In that case how can it be the "Lord" of or rule over a whole zodiac sign comprising of several stars ?
Then again the idea of enmity, friendship between planets, exaltation, debilitation, aspects of planets, ownership of zodiac signs by planets etc. etc do not have any logical or scientific basis. Considering the above facts it may be concluded that the ideas of various yogas are also all imaginary and do not have any logical or scientific basis. Correctness or mistake in predictions are all matters of pure guesswork. Besides this, even Sun & Moon are considered as planets and Rahu & Ketu are also planets in astrology though according to science Sun is a star, Moon is a satellite of earth and Rahu & Ketu are imaginary points only. If you wish to have a detailed study on the subject please log on to : roymukherjeearun.blogspot.com. and go through the articles therein starting with the one titled “Vedic Astrology”..