Page 157 of 5th ed. rules clearly states that adders advantages are applied to powers only after all adders are applied. Then, endurance cost is determined by the total active points in the power, after this result is obtained. Unfortunately, this strikes me as a grevious oversimplification. In addition, examples in the the text of the book also seem to contradict this rule. For example.....
1)bottom of p. 73: Kasdrevan has Aid 4d6 with a +2 advantage to affect "any characteristic below starting value". Later, he uses 10 experience to boost the amount he can add by 20 character points, from 24 to 44. Where's the multiplier here?
2)p. 83: Golden Eagle started with 20" of flight at x non combat speed. However, he then BUYS 2 more multiples for 10 character points, giving him x8 non combat velocity on his 20" of flight. The final sentence in italic then reads, "His Flight costs 4 END, regarless of whether he uses Combat or Noncombat Movement." This is at least entirely consistent with the rule on p. 238, which states that characters using non combat movement spend the same endurance they would have used at combat velocities.
I think that the multipliers for power advantages should be applied to the adders in question on a case by case basis. In the first case above, it seems clear that if the character points gained from the boosted maximum are applied to multiple statistics, just as the character points gained from the 4d6 would be applied to multiple stats, then BOTH the base cost for the dice and the adder for the boosted max should have the multiplier for the advantage applied. However, if noncombat movement doesn't cost extra endurance, then why should an advantage such as red. end. cost be applied to the active points for extra non combat multiples? On the other hand, if a character has 4 noncombat multipliers and pays a +1/4 advantage for rapid noncombat movement, then he SHOULD pay the advantage on both the base flight and ncm costs, since both are affected by the ability to accelerate more quickly to full noncombat speeds.
Here's another hypothetical example-
Suppose a character with a 0 end persistent force field can, by force of will extend his force field around an object he is carrying, or around another person (10 pt. adder). Suppose that since this act requires conscious effort on his part, it costs him endurance, and the extended forcefield disappears if he is stunned or knocked unconscious. Is there any conceivable reason to pay for the 0 end or persistent advantages on the 10 pt. adder? I say no....
To sum up, I would be thrilled to see an official Hero System ruling stating that advantages be applied initially to the base cost of the power in question, and to the adder, if and only if the adder in question is ACTUALLY AFFECTED by the advantage in question. Short of this happening, I am looking at making this a house rule in any case. Has anyone else out there looked at this problem and reached a similar conclusion? Or perhaps an entirely different one?