Take my advice as much as you paid for it, it's worth about the same :)

On the fly math is always scary, especially in online forums where people are quick to be pedantic (I would never do that).

At the risk of being completely pedantic, if it's 65% efficient, it would be need to dissipate 15.38 watts to move 10 watts (10/.65).

Or, I could be completely misreading what you said, which is highly likely.