I don't know where this belong, but for posterity:
Percentage bonuses are first added together, then applied, then rounded up.
Example:
With 22 base etheric power, smoldering coal (25%) and dark wind (20%), we have:
coal: 25% of 22 is 5.5, (rounded up would be +6) total with just coal (no wind) would be 22+6=28
wind: 20% of 22 is 4.4, (rounded up would be +5) total with just wind (no coal) would be 22+5=27
coal+wind: 45% of 22 is 9.9, (rounded up is +10) total with both is 22+10=32.
One *could* expect each item/effect to calculate its bonus separately and then add the results (which would lead to 22+5+6=33), but that doesn't happen. You can only get up to +1 from rounding errors from all sources together.