I had a further thought on whether a mixed order unit should retire its non-archers to the back, so I have the following questions / suggestion.
If a unit is in combined order, then the non-archers are stationed at the front with the archers at the back. As per p.42 3rd para under combined units, these archers do not get the second row bonus when shooting.
However, with a mixed order unit, there could be more than one row of archers and they are instead normally stationed at the front, so I presume they should get the second row bonus when firing (the Mixed order rules do not specifically cover this). If, after a charge and melee, the archers are left at the back. So, would the second row bonus for shooting apply to 2 rows of archers at the back of a formation?
If the non-archers are later retired to the back then the archers are again at the front and would they then have the second row firing bonus?
If they can have the bonus when the archers make up the front ranks but not when they make up the rear ranks, that would be an incentive to lose half a move to reform the mixed order unit back to having non-archers at the back and archers at the front.