Dorkus,

Maybe pikemen should be used in a deeper formation for best results. I guess, if the pikes are better than the unit they are engaging, you can set up in a wide formation without concern, but, if they are facing a tough opponent, deeper would be better. However, with a shorter frontage they would be more vulnerable on their flanks.

Two other things crossed my mind concerning pikemen in hold formation:
1) Fatigue level of a unit is the average of the fatigue of all the men in the unit. Many of the men in a pike unit are involved in the combat, so the unit will fatigue faster than a spear unit where less men are actually engaged. In a spear vs pike engagement, the units will usually go though all the stages of fatigue before the combat is resolved since they are both highly defensive statwise. Once you get to very tired, unit wide att/def combat penalties start being applied.

2) I've noticed that a charge by a unit in hold formation is not very effective. It must be because only the men in the front row engage and get the charge bonus. Any unit put in hold formation would suffer from this. Pikemen and spearmen are usually used in hold formation, but, if you want to get the most out of the charge itself, it would probably be better to switch them to engage-at-will. I'm not suggesting this for a unit with a narrow front because most of the men will just pile up behind the first couple of men an loose their charge momentum anyway.