This plant thing is odd, Moneywort (Bacopa monnieri) from petschmert is a good deal and grows great for me, the odd stalk base rots away but then it thrives as a floater. Other curse it.
Yes- The depth from the surface is the limiting factor in having it work. If you have a health stream of bubbles I would consider it to be working fine. I buy pretty cheap pumps and they run multiple airstones FWIW.