Wouldn't waste my time. Surely there are bigger fish to fry. In 30+ years of auditing I've yet to find a meaningful KPI, frankly. The fact that IA is in the "performance Measurement" section of the standard gives you a clue to the fact that it's a pert of performance evaluation, not a core process for the customer or business. IMHO - find something management want to get benefit from measuring...
BTW - your external auditor is plain wrong!
