I played my first game last night using the Lobositz scenario. BUAs on the Austrian left caused casualties as cavalry charged past from long distance. Didn’t seem like a big deal but it did impact the units and covered a large part of the battlefield. The reach seems long for a BUA when men are in buildings and along street barricades. It is not volley fire. Can you really fire out that far from a BUA? I definitively can see firing out per the rules on units charging in. Would think only short range fire should be allowed.
Maybe I am am too liberal with the cross-fire rules?
Personally, I have no problem with fire from a BUA being at full range. The protection afforded to the defenders and the chance to rest weapons may well cancel out the fact that volley fire was problematic - and of course firing by volley doesn't really increase the range of a musket.
If you feel crossing fire is too effective, I suggest applying the -1 modifier for a difficult target at all times when using crossing fire. In practice, I often find the fleeting targets of crossing fire end up deserving this modifier anyway.
As for Lobositz, consider the following quote on the initial Prussian cavalry charge given in Duffy's By Force Of Arms:
"The cavalry was the cream of the Prussian mounted arm, and the Austrians let it advance without opposition, 'but after they had lured the enemy close enough, not only did they open up a heavy fire against the flank from the village of Sullowitz, but all the Hungarian infantry (probably Croats), up to now hidden in the sunken roads and ditches in the plain, came to life all of a sudden..." (p.25).
The flanking fire from Sullowitz is mentioned in most accounts of the battle, muskets as well as artillery (see the Wikipedia article). Don't forget the full 30cm range includes battalion guns. If you prefer to limit the fire to 20cm, you are of course welcome to do so. In my opinion, the rules as written represent what occurred on the day of battle reasonably well.