Yes, I support your comment, 反腰發力 is the core of Fu style martial when my Master taught me 靈貓捕鼠 of Liang Yi quan yesterday. I felt the 2 ways of pushing and twisting power sourcing from waist very powerful. I guess that they are as same as 八卦正宗, it is the core of Fu style martial.
I have not practiced 八卦正宗 yet. Is my supposition correct please?