There is no 70% or 80% base for contribution of PF but PF should be contributed on 100% of the salary. Here salary means the amount of remuneration agreed with the employee in return for the services/labour that he puts. Obviously, any incentive which is earned as a result of satisfying certain conditions, like achieving certain sales/production figure, goals etc or overtime wages which is also an amount earned on satisfying a condition of working beyond a certain fixed period per day or week, only are outside the purview of wages for paying PF.
Though the EPF & MP Act excludes HRA from wages, the same applies only to such allowances which are paid to those who reside in rented houses as part of their employment.
You may have different components in your salary,like Basic, Dearness allowance, HRA, Special allowance, travelling allowance etc. A very simple test to decide which of these components of salary will qualify for PF contribution is to see on which component will you deduct Loss Of Pay if an employee remains absent without pay. Certainly, it is not the basic alone or Basic and DA alone which is not paid when an employee is on leave without pay but the entire component is not paid. As such the total salary is the salary which qualifies PF contribution. HRA, if paid separately to those who stay in rented houses, will obviously be paid in full even if he is on leave. Therefore, only such HRA will be excluded from salary.
If the total salary exceeds Rs 15000, naturally, the employer can restrict the PF qualifying salary to Rs 15000.