I also recently found the exact same thing! I created the "schnorckel", a way to top feed my babies without putting a punp down in the bottom of the res. I was too lazy to set them both up, and the one with the schnorkel LAGGED while the one that got neglected TOOK OFF!. As soon as I removed the schnorkel from the smaller plant, BOOM! She's starting to catch up.
I think I'm done with top feed. I just keep the solution within a half inch of hte bottom of the cup, and the bubbles from the aeration stone keeps the pebbles moist, and the roots growing out for more soliution!