Big power loss in low position . . .

If I have a bar drop of more than 4 cm, or a reach -- tip of saddle to bar -- of more than 53 cm -- and I mean by just 5 mm -- my power output drops by 20 - 25% for a given perceived effort. (I know power drops as you get lower, but shouldn't it be more gradual?) Is this just due to my ridiculously short torso? (I'm 73.5"/187 cm tall with 36"/92 cm inseam.) Or, could this mean my saddle positioning isn't ideal? (With all the fiddling around I've done, I would think I would have come across the right combination by now.) Or is this just how some people are? The position is comfortable, not complaining about that. Just can't stop wondering if it means something with the fit isn't correct.