I did it - I upped the difficulty...eek!

Damage:
All Power Combos have a "base" damage based on the combo level, which is simply the total power level of the source and detonator. The base damage ranges from 100 (for a minimum combo level of 2) to 250 (for a maximum possible combo level of 12). Note that for purposes of combo levels, multiplayer Ammo Bonuses always count as rank 1 powers. This is in contrast to single-player ammo powers, which use their respective power rank for the sake of calculating combo level. This base damage is then multiplied by a factor dependent on the game's difficulty, scaling with enemy health.[2]

Narrative: x.5833333
Casual: x.83333
Normal/Bronze: x1.5
Hardcore/Silver: x2.25
Insanity/Gold: x3.375
Platinum: x4.3875
Note that this scaling means that, as difficulty levels increase, the relative importance of combos for a power-based class's damage output increases dramatically. For example, in multiplayer a maxed-out combo will do only 375 damage on Bronze but an astounding 1,096 on Platinum. This also has the ramification that while ammo powers may be useful from a single-player/solo perspective for priming/detonating combos at will, it can severely reduce the total damage output of a power-heavy party in multiplayer.

The combo damage is further modified based on its type and on whether it is damaging armor, shield, barrier, or health as noted below (e.g. Tech Bursts do 2x damage to shields). Any debuffs on the target receiving the combo (such as Sabotage's Tech Vulnerability) will also affect the combo damage, if applicable.

The combo damage is otherwise completely independent of the actual damage or damage bonuses of the powers being used, unless it is a damage bonus that specifically mentions combo damage, such as Warp's Detonate evolution. Power evolutions that enhance combo damage for both the source and the detonator powers do stack if they are both for the same combo type (e.g. Warp and Throw both so-evolved results in an especially powerful detonation). Note that Snap Freeze's Tech Combo and Electric Slash's Detonate evolutions are bugged: Electric Slash's Detonate evolution does not actually affect combo damage, and Snap Freeze doubles damage for any Cryo Explosion the N7 Paladin primes when he chooses Reach at rank 4. As for the Alliance Infiltration Unit Infiltrator, she has to select the Tech Combo evolution, which doubles combo damage for any non-biotic combo (i.e. fire, cryo, or tech) whether priming or detonating. Electrical Hammer's Radius & Combo evolution by contrast only affects combo damage when used to detonate.