When looking at the picture keep in mind the leader to the SNG and Lead is Mono,(Made for a better picture using Braid). Not my picture BTW.
I also tie a U20 to a Duo lock with appox. 24" mono leader. This is attached to the main line and allowed to slide down.
To control the depth your U20 runs put two beads on your main line above your weight slider. Either tie a rubber band or a bobber stop between the two beads, (I prefer a rubber band as it does not pull through the bead holes as easily as a bobber stop). Before deploying your gear slide your rubber band or bobber stop to the desired depth.
when you slide your U20 down your main line it will work down the the bead and stop.
I like the U20 to run no more than 12" under the surface personally. You can add bait to the SNG if you are inclined. I prefer to run them naked.
36th SPS Bitburg AB, Germany 90-94.
Desert Storm Vet.
CCA Mt. Hood chapter member