Many recipes call for a lower temperature in a fan oven (usually by 20°C), which makes sense as these ovens transfer heat more effectively. However there would appear to be exceptions:
When the conventional oven temperature is only just high enough for browning – the Maillard reaction needs ⪆ 140°C while caramelisation of most pure sugars needs ⪆ 160°C. A recipe reducing from 160°C to 140°C would therefore seem to result in much less browning when equally cooked through. But keeping the non-fan temperature would result in overcooking.
Sterilising jam jars in the oven (common/official advice for hot-packing jams, chutneys etc.) relies on the surface getting hot enough to kill anything that could be living on them.
I'm sure there are others.
How can we identify and deal with such cases? Is there a good rule of thumb for when to lower the temperature and when not to?