ancient armies typically arrayed with more width than depth and the rules reflect that - a 16 man unit gives you 2 ranks of 8, which is ok for smaller games (or 12 models equals 2 ranks of 6)
In my Spartan army my supporting hill tribes are 16s and the hoplites are 24s, so you could ratio this down to suit.
There would be no harm in just having an 8 model unit of course, if all units on both sides are of similar sizes you will have the same challenges - you might find it effective to give each model '2 lives' so you can cope with some attrition.
Alternatively, you try using a smaller 'scale' and taking 1 figure to represent 2 models, so your 4 fig frontage has 8 strikes, you might need to half all the movement distances to get the correct feel though - not ever tried it, just a random thought really
Anyway, hope some of that helps and enjoy the games!