Indirect Fire?

I find it odd that ancient and medieval rules don't seem to allow for indirect fire from archers.  After all there seems little point in not protecting them behind infantry and letting them shoot at an approaching enemy prior to contact.
There's a bit in Thucydides where he says he deployed archers and javalinmen within a hollow hoplite square. The light troops being unable to withstand contact, they were protected and they fired over the heads of the hoplites onto the approaching enemy. So if it's good enough for Thucydides...

I roughed out a system for the two rule sets I commonly use thus:

The flanking archer elements can be moved out to the side and engage in direct fire on any following enemy once the beaten zone has been passed, leaving the centre archer element to still fire indirectly. Not tried in a game yet but hopefully soon.