area and duration determine the size and how long the hazard generated lasts afaik, while the magnitude of the efffect delivered by the hazard is determined by the magic effect of the spell that the hazard itself casts.
For the life of me I can't figure out what the magnitude of the spawn effect is for though. Apparently it is used, as the blizzard spell (for example) has the MagicDamageFrost keyword, which is used by the augment perks to determine if to multiply the magnitude of the effect, and also under the spellmaking tab the power affects magnitude box is ticked...
Thanks for the help
