The original War-Law gave xp guidelines for the units involved... but none for the leaders.
I suppose the main factor here is to assess the risk to the character (General) involved... *o.5 if little or no risk... none if at no risk. Further factored in is how many times that he has successfully used the tactic that caused the victory.
As far as Idea points, these are shared out between ALL those involved, yes? So, relatively speaking those involved get a greater proportion anyway it wouldn't all go to the general, some would have to go to the unit leaders, some to the NCOs and some to the grunts. True a large proportion should go to the General, but by the time it has been diluted by the above factors it shouldn't be a massive amount.
However. Generals do tend to be rather high level and these xp awards aren't everday events, so a large award isn't really that threatening to game balance due to the amount required for the general to progress.