I don't think much of the problem arises from range, so much as if it's LOS or not. I mean, it'd be near suicide to use a pie plate on a target that is closer than 12", b/c it can still scatter....straight into you!
As for firing indirectly even if you have LOS, why bother? The scatter is the same as firing directly from an ordnance weapon. The only difference is that if you fire it indirectly, you cannot fire it below the Minimum range.
Basically, if anyone by some freak accident got close to your bassie (and you have LOS), you COULD shoot them indirectly, so long as they were outside 12". Or if they were within 12" you could shoot them directly. Just be careful b/c if they're w/in 12" and you put a pie plate on them, you the dice gods ain't favoring you, you're going to kill yourself.
So OP, to summarize (with some new knowledge brought to light by the above posters):
1). If the enemy is out of LOS, use Indirect fire and the rules for barrage weapons.
2). If the enemy is in LOS:
a). And is outside the minimum range for firing indirectly (i.e. as stated above for the mortar, more than 12" away) feel free to fire directly OR indirectly b/c the way to fire it, scatter it, etc. is the same. In this case, if you fire it indirectly, consult the barrage rules. If you fire it directly, consult the ordnance rules.
b). And is INSIDE the minimum range of firing indirectly, than fire directly. And consult the ordnance rules.
That basically answers the quandary of the bassie. Depending on range and LOS, you have 3 courses of action.
Hope this helped and clarified it some.