I also do not know how much ammunition they carried. I would think it should be okay to increase it to 40 at least. With 10 pieces that would make a total (10*40=)400 arrows as opposed to the (8*30=)240 currently, making them potentially 66% more effective, plus the increased effect that the higher rate of fire the increased number of pieces would give.

I'd be wary sending my general into a battle where two units of those were hunting for him .