Soon I will have my PKs in a battle against King Idris and his knights. They have managed to get the help of three counties (Jagent, Dorset and of course Salisbury). One of the PKs is named the army commander (he serves as the Marshal of Salisbury). I am planning on using the rules from the BoB, but am a bit concerned about the battle events.

You must roll a 3d6-10 to determine the effect on the Army intensity. Combined with the fact that a group of PKs can mostly lower the intensity by a maximum of 2. It seems that the battle events will have a greater impact on the result that the actions of the PKs. thus a random roll will determine the outcome of the battle not the skill and tenacity of the PKs.
I am thinking on changing this, but before doing so I would like some feedback from you.

How did you feel the battle events influenced the battle in comparison to the players?
Has anyone changed the rules here?

Well, I came up with my own rules for battles, especially small ones where the PKs tended to be in command.

In my understanding, the Book of Battles is intended for larger Battles, with thousands of participants. Thus, it is easy to understand why the PKs' actions get 'muted' by the larger battle raging around them.

I haven't run any battles using the Book of Battles, so I am probably not the best person to talk about that... But off the top of the head, I don't see a huge problem increasing the PK effect, at least for a bit.

What I tend to do is to try to give the PKs something important to do, like capture the enemy standard or one of their leaders or something like that, in extended melee round. I.e. run it like a normal combat. Otherwise, the battles tend to be, well, a bit boring. And easy, compared to facing comparable enemies in regular combat.

I haven run BoB2, but in BoB1, all large battles tended to end in draws. There was a lot of errata on the way Intensity interacted with withdrawls and rout, but it was hard to get a handle on. What I did, was that I just fudged things. A lot. I either just fudged the Intensity in the favor of the side that won according to PGC, or I just said "the other side routs" at the end of the battle, whatever the Intensity.

BoB1 works really well with Small battles. Larger ones, no, not in my experience. And you have to make a decision if you use it: will the result of your gaming session decide the outcome of the battle or will PGC trumph that. BoB will play havoc with the story line in PGC. Be advised.

In my experience the randomness of the random roll tends to even itself out.

It is with great risk that the players can end the battle in their favour, no matter how strong the enemy. They "just" have to reach the enemy camp. I had this happen twice now, although I interpreted the rules in the player's favor a few times.

The event roll does make things interesting in my opionion. After all, this isn't a RTS where you can tell everyone directly what to do. It IS a brutal and confusing clash of two forces and the best you can do to have the battle end in your favour is by improving your position on the battlefield before the battle itself happens.
Good position, more men, better equipmentn etc. which is represented in the pre-battle adjustments to the army intensity. And still, it can go either way.

I haven't found the standard combat to be particularly dangerous unless you are facing a monster or an impassioned Knight. Battles using Book of Battle on the other hand seem *very* deadly.

I changed the battle events to 2d6-7 instead of 3d6-10 and it worked out well in my experience.
I want to tell a story and the system should support this. In this case the battle events were the same as the unit results.

I used some gameplay before the battle and they managed to get a slight advantage on the enemy (Army intensity started at 16)
First charge was successful and they manged to split the army of King Idris. (unit result -2 to army intensity)
They smashed into the enemy and pushed a wedge between the flanks of Idris army. (events -2 to Army intensity)
The next round had an opportunity and were able to flank a unit of notable knights, unaware of their situation.(Unit result -2 to army intensity)
Third round event the push of drove deeper into the enemy (Event -2 Army intensity)
The PKs continu to fight the unit of notable knights, but now the enemy is aware of them their attack is less effective. They still win, but no change to army intensity
Luckily their army is very good and they drive the enemy before them (Event -5 Army intensity)
As the army of Idris retreats slowly the knights follow (Unit result -2 army intensity)
Driving the enemy before them the army of the PKs drive the invaders back (Events -2 Army intensity)
Finally the PKs pursue the enemy of the field and capture the enemy camp (Unit result -2 army intensity).

I must say that they were lucky in the events going their way, and I had hoped on a bit longer battle, but it was fun and it made good storytelling.