Predisposition of 8 Mansions

Predisposition - is a very big Concept with various interpretations. The common synonym would be inclination. Various method in FengShui has various means of predisposition for an individual. For example, in the 8 Mansions, individuals are classified as East and West Life predispositions. An East Life person ideally must live in an East House. Similarly, a West Life person must stay in a West House. Mismatching denotes bad FengShui. 

Common ways of profiling such predisposition is as the following example: -

A male born in 1972. Numerically, add up 1+9=10, round up to 1 plus, 7+2=9, giving a grand total of 10, round up again to 1. Take the constant 11-1=10, round up to 1 again. So this person has the predisposition of 1, taking the Gua imagery of Kan.

Have one ever ask, where the hell has this formula comes about? 

Why a male  predisposition must be subtracted by 11 while the female predisposition must be added by 4? What is the basis of this predisposition?

Here is the CLUE: -

1. 8 Mansions has the similar SanYuan roots as its counterpart XuanKong. The basis is within the LoShu of the Greater SanYuan and nothing even closed to ErYuan. A person's predisposition must be determined via the upper, middle or lower Yuan of its year of birth.
2. A person's gender determines the YinYang cycle of the Greater SanYuan.
3. Also matching the GuaQi of the reigning period.
4. Replacing thus, we obtained the Gua number or predisposition of the person.

So, to simplify matters, such a complex calculation has been made into an arithmetical formula. Unfortunately, without realizing such, do we still call 8 Mansions as a SanHe method?