What is an 'archer'?

[Agema]

My experience with archers is that they tend to go for the nearest unit that qualifies for their targetting orders. Thus small decoy units at the front often draw fire.

This makes them differ from spells, which almost invariably look for most damage. Trying to distract mages with small 5-strong units pretty much never works. Firstly spells with AoE more than one cannot maximise damage, secondly low-prec spells are likely to miss. Consequently, mages will drop them into big unit concentrations.

Also, bear in mind these sorts of things also make cavalry much less likely to be targetted by mages. There are 3 infantry per square, at about 10HP each = 30+ total. Cavalry only fit 2 per square, as almost none have 15 or more HP, so have a lower HP/square. Add to that, heavy cavalry are often better armoured making them even likely to take less damage, and also operate in smaller groups so low-precision spells are more likely to miss.