Bell siphons don't need the reducer. Mine are about as simple as it gets. 1" standpipe, 2" cap and 1/4" aquarium tube breather. The part that most people don't consider is the plumbing. You need a little back pressure to get it working right to kick.
Think about your toilet. Add water at a slow rate and suddlenly it flushes. Once it pushes the water over the trap, away it goes.
I put screening around this to keep the rocks out.
This needs about .5 GPM to trigger.