In the universe of finding mathematical precision, three paths seem to prevail?
The +/- 15 sound like the median approach of finding central tendency approach in a *range*
The averaging approaches such as Porphyrii/Sripati, Placidian system and many others seem suspiciously like the mean approach of finding central tendency?
Kind of like borders of a or many-a-Nation?
Depending on current political divisions etc, same or similar *people* get divided by political boundaries and the world has seen many examples of such, historically and so on?
The Natural Division seems to simply be one that treats a Rashi as a Celestial boundary? Which is what many siderealists believe in and utilize (A)
The Mathematical/trigonometrical divisioning remains up for greater debate and hence we see across the east and west dozens of house division systems in Europe mostly and a few in India as well. Chinese and Burmese astrologers went to other approaches entirely!
To assuage the GREAT DIVIDE and trying to bring the khichdi to appease all and everyone to share the Celestial Meal together, perhaps the approximating/averaging systems (EHD, SHD, PHD, EPS, ZHD etc) came together...?
The greatest problem with the whole sign sidereal system has been ayanamsha which has varied over a few degrees and it is the cuspal births that have remained the mainstay of or at times the 'bones of contention' of all times...?
The third approach, MODE based is where empirical and practical observations etc come to play? Not fool-proof but on Planet Earth and Mrityu-Loka, the best approach as any practising scientist can vouch! And a lot of reading and continuing education...
THAT is what you must first seek and search and determine, given your brilliant mind and true passion, without worrying about what others found or insist is the ultimate truth whether they learnt that from some teacher or an astrologer-ancestor, whoever...?
All questions and doubts shall diminish and you shall find the path that you are seeking, Seeker...!