What the expected temperature veration between shelfs in a fan oven?
Isn't the point of a convection oven to move the air around and create a more consistent environment in the oven?  People get caught up with the idea that an oven needs to be precise, when, in fact, very few ovens are accurate (with respect to the number on the dial and the actual internal temperature), and it is not uncommon for the temperature to range significantly within a cooking cycle.  It is also not uncommon for the temperature of a standard oven (no convection) to range in different places within the oven.  Ovens are not precision devices.  In fact, some argue that we should stop worrying about exact oven temperature (I whole hardheartedly agree), and just think in terms of three or four basic ranges (low, medium, high...or...really low, low, medium, and high).  The article specifies the temperature ranges.  Nothing that is cooked in an oven requires more specificity than this.

It seems to me, you've gone above and beyond to please your tenant.  Now, it is up to them to understand oven cookery.