12th House is like last compartment of a train while ascendant ( first house) is like the engine of a train . Normally 12th house is feared because it represents end , expenses , loss , termination of the existence . But once the train reaches a destination , the engine is again shifted to last compartment for new journey . So, 12th house always has the prospects of becoming ascendant .
After existence finishes , esoteric things still remain ( like spirituality , memory , soul ) so 12th house also represents esoteric world . If ascendant represents your native roots , then 12th house represents being away away from all that is your native background .
Therefore , when planets are placed in 12th house , they show the linkage to something which is distant but still yours . For example , if 5th lord of education is placed in 12th house , it would normally mean that you will lose the benefit of education at your native place but if you go to a distant place , you may receive good quality education easily .
When there are many planets in 12th house or 12th house owner planet is placed in any other house , it means that subject matter of that house is available easily at distant , foreign place but not available at natal place . To gain from that, one should relocate away from the birth place and that will make 12th house work as ascendant .