Manual soldering - solder wire diameter and soldering iron tip size for different component sizes

We recently had a discussion with customer's QM - he claims that calculations for a proper solder wire diameter and soldering iron tip size (and temperature) have to be performed and documented for all manual (T/H) solderings (based on component size, plated through-hole diameter etc.).

We usually let our employees to use their common sense and decide which is the most proper size of the tip / solder wire (of course, employees are trained both internally, and acc. to IPC / workmanship standards). The target is to keep the temperature as low as possible while maintaining enough temperature to quickly solder a joint (2-3s), so this also leads to tip size (basically - bigger is better). But - calculations for each component..? Does anyone actually do that? How are these performed?

Thanks!

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