There can be no doubt, though, that the action of the popper above created so much attraction that it made the dropper more effective than if I just fished the dropper.
Not doubting, just concerned with accuracy.
Did you actually fish with the fly you used as a dropper, by itself? The experiment isn't complete without an equal time of fishing just the dropper as a control. There's too much evidence that fish will hit a single fly to say they'll be MORE inclined to hit a dropper under a commotion causing hopper, etc.
Yes, I fished quite a bit with just a fly, and just a popper but by far the best presentation was a popper (one of Mike's) with a San Juan worm 20 inches below it.
We fished for five days. Four to five hours in the morning, starting at five. back to the cabin at ten for breakfast and a nap and then back out on the lake from five till dark (10:00). We had lots of time to try different things. We tried foam bugs, dries, woolly buggers, really everything in the box.
At times we could see the fish and I would cast past them or even right on top of them and wait till the rings dissipated. The fish would gather around but not really bight, then as soon as I popped the popper they would really get going. We caught some fish on almost anything but like I said, the popper/dropper was the hot thing on this trip.