Re: Half and Quarter Stacks
Prefer, no. Use, yes. Typically a minimum of 8 units, sometimes pure ashigaru and sometimes ashigaru mixed with katana or naginata samurai. They make good support forces, nipping in to take and hold a nearly empty castle after a larger army has defeated the main enemy force in that area, speeding forward to assume garrison duties so my main army can resume the advance, or rampaging through lightly defended enemy areas.
Re: Half and Quarter Stacks
General, 4 yari ashigaru, 4 bow ashigaru, 1 yari samurai: still undefeated in my campaigns :D
In mid campaigns I simply add few 1 naginata and 1 katana samurai to that and usually move with 2 of those armies, helping eachother if needed...