Reducing effects of attrition in combat.

[Gufnork]

I've been bothered quite a bit by how effective sheer numbers are against superior units. The best way I can think of how to tune it down is to change how power is reduced when you lose hit points. I was thinking of something along the lines of 50%+current hp/(2*max hp). I don't know how to do that however, so I wondered if anyone could give me some pointers.