Odds for attacker?

[Colonel Talvela]

In QBs:
Probes give attacker +30% (I believe)
Attacks give attacker +50%
Assaults give attacker +70% (close to it)
I think most people are comfortable with these values, although terrain, weather conditions, # of turns plays an important factor.

For custom scenarios - it is purely up to the designer. The attacker could have less points the defender.

mostly it depends on what you are looking for. Do you want balanced games to test your tactical skill? You looking for historical fights.