Duncan,
That is a shame, many thanks for helping with this. 
It's not necessarily a shame, depending on whether you can take advantage of it.
For example, I used an army with massed Wb (O) in four ranks, and I was facing an army with massed Irr Kn (F) in one rank plus a few reserves.
I deliberately let the Wb go impetuous to break up their formation when they were close to the Kn. So what happens:
1. If the Kn move to make contact in his bound, his Kn line up against my slightly advanced columns, meaning every second Kn fights against a double-overlapped Wb: very good chance of killing the Wb. What happens then? Those Kn pursue into contact with the second rank of Wb.
But, now in my next bound those previously victorious Kn are double-overlapped, and the Wb have a reasonable chance of knocking over one or two Kn, opening up gaps the Wb can exploit. And because adjacent columns of Wb are not aligned with each other, every combat involving the Kn will have some overlaps; this pulls down the combat factors, making it easier on average for the Wb to double the Kn, but no easier for the Kn to outscore the Wb for the Quick Kill. The (theoretical) result is that Wb actually have a pretty good chance of defeating the Kn.
2. If the Kn hold in place and let the Wb make contact, then the combat takes place with a straight line as the Wb conform to his Kn. But, of course, the (F) factor for the Kn makes them a touch more vulnerable if they lose a combat, so there's a chance that my Wb may destroy a Kn or two before his bound.
Now, obviously, this is a very specific example (it came from practice games for a themed competition), but it points to a general rule - you don't need to fear impetuousity in your army if you have plans for your impetuous troops that takes advantage of their impetuousity. It just needs to be carefully managed.
So, for example, if you have irregular impetuous in an army with regular generals, it's probably best to place those troops under the C-in-C as his free PIP can be used with all troops, while the free PIP for regular subs can only be used with regular troops.
Another trick is to place 0.5ME impetuous troops (like Wb (F) or (O)) in a fairly small command and support them with a couple of 1ME elements. If you lead with the Wb you'll find you can lose most of the Wb before the command breaks. For example, I've fielded Anglo-Normans with a small Welsh ally command of Ally-general, 2 Cv, 1 Ps, 9 Wb and 1 baggage for a total of 12ME. The Wb fight in three ranks while everything else stays behind the Wb. The command becomes disheartened when its losses reach 3.5ME, which requires the loss of 7 Wb. If I can launch this command at some enemy infantry and keep their flanks covered, they actually have a pretty good chance of breaking through, even if they take heavy losses in the process. (And if the enemy has little or no infantry, the command is small enough to simply send flank marching without weakening the army too much.)
If you have mounted impetuous troops (that is, Kn) remember that there are situations in which they won't move spontaneously - for example if they're in ambush or in difficult terrain. If you think placing in them in difficult terrain is silly, remember that they can use their good terrain move distance if that would allow them to get entirely into good terrain. For example, you might be able to place a Built-Up Area in a suitable part of the table, then place two ranks of Kn at the edge of the terrain; their good terrain move is 10cm, while two ranks of Kn are only 6cm deep...
This is a game which rewards some lateral thinking.
Good luck!
