Dear Mbsmani.
There is no law prescribing any formula for fixing a ceratin percentage as basic pay and even the Minimum Wages Act does not interfere with the structure of salary so long as the wages paid by you are not less than minimum wages.
It is entirely within the realm of the employer to fix the quantum of various components of the salary/wages and no one can insist that P.F contributions shall be paid at least on minimum wages.
However the employer shall adopt sound principles of wage fixation, having regard to industry-cum- region formula and the degree of responsibilities, the level of skills required to perform the job etc.
As per the normal practise, Basic is fixed at 30% to 60 % of the basic salary. 30% being the lowest and 60% being the highest as a thumb rule.
Only make sure that the basic +DA is equal to or more than the minimum wages applicable to your industry and location.
Regards,
Ashutosh Thakre