I switched from the standard pop bottle baffle to sponges due to concern about sharp edges. Since I made the change, boyfish has been swimming near the surface more, though it looks like there's a pretty strong downward current thanks to the sponge not fitting directly against the outflow.
Here's a video showing the current setup and the signs of the water's flow in the plants and on the surface.
Any thoughts? Boyfish avoids swimming directly under the outflow now, and the one time he did go under it, he was pushed down a good inch by the water current.