Salvage modules using more power than reported?

I place a single row of 20 salvages, no slaves.....and then a second....which bumps my power usage by just under 600 power. If the tick rate is .03 per second, that 33 ticks per second, and at 0.4 damage per tick, thats 13.2 damage per second per module, or a total of 264 for that stack. The second stack should have no more than 10% additional if the penalty has not been changed, yet it is over 100% more.

Any ideas? Is this a bug?