Imo it is always best combo if you fortify 2 melee, and soften up enemy from range. So for every 2 melee, 1-2 archers, depending on positioning, if archer can be flanked and killed, sometimes 3 melee for one archer.
But, you cant stack more melee units on the front line, so the only way to increase damage output is to have some range.
If you fortify, you get heal this turn, this means enemy hit you, but at the same time he used his turn to heal, so after the turn, you get some hp back and he dont.
At the same time, for combat purpose, you used your terrain defence bonuses (cross river attack, hill, forest), and his damage was mitigated, so if im not expecting to crush barbarians, i kinda prefere, for them to
hit me once or twice, and then i "step into action"
Also for this reason i always go Heal promotion route for archers, since they dont do enough damage to get the job done alone, but at the same time, front line meat shield healt faster, sustain is really important.
Also 1-2 turns later, enemy is soften up to the point you can kill him with flanked units. For the same reason, early game i expose my archers for melee attacks, if im sure they survive for extra 4xp per hit taken.
Also it is good to make offensive roads in specific defence positions, so you can replaced damaged unit with fresh one in one turn (im talking new raging barbs, i stopped playing them when i saw they killed
some cive, they can be overwhelming)
It is also worht tho have some horse units in the back, in case you cant get the kill, and they are also very good to give you instant flank bonus, or block units to retreat fast with their zone of control.
In rought terrain sometimes it is better to have some skirmisher units, since they can enter hill, hit, and go back, effectively working similar to "Indirect fire" archers.
Generealy its good to have some 2-3 skirmishers squad, as a form of fast respond, they can take 1-2 hit, thus preventing from pillage, and in this number they can hill some unit.
