in case of a firm, each partner is said to be appointed as the auditor in the firm's name on behalf of the firm. It is not the firm but the auditors of the firm who can undertake Tax Audits. So the ceiling is in respect of each of the partner's and not for the firm in aggregrate. So each parnter can take only 45 tax audits only on behalf of teh firm .
section 224(IB) clearly states that each in case of a partner the number of company audits would be 30 for each partner. So total number of partners multiplied by 30 in case of each partner and not collectively for teh firm would be maximum ceiling that the parnters would be taking the audits.