Thanks Greg,
I too find this maneuver one that benefits from having a good foundation in the individual components, specifically well controlled circuits. It's also another move that requires precise collective control. Slowing down the physics in the sim and breaking it into its core movements also helped me. As with a lot of the transitional maneuvers I find that identifying and then focusing on just those things the sticks do in the transition helps me develop a rote ability to do the move. For example lets take a backwards snake with a upright CCW circuit into an inverted CW circuit. Because steady state circuits are a generally fixed input move we can simplify as follows. For upright backwards CCW we are holding in this case a positive collective with left rudder (up/left) and a forward elevator with a mostly neutral aileron (up/center). The second part of the move is the inverted backwards CW circuit which requires down/left on the left gimbal and a back elevator with a mostly neutral aileron back/center on the right gimbal. This means that the transition requires the left gimbal to go from up/left to down/left. The right gimbal must transition from up/center to down/center, but there is a little more needed on the right gimbal for this move. Because it requires a roll from upright to inverted and then back the other direction on the next transition the right gimbal must move roughly in two line segments. For the upright to inverted transition the right stick goes from up/center to center/right and a second line to back/center. I find thinking in terms of clock positions helpful as well here so we are going from 12 to 3 to 6 O'Clock. In the next transition back from inverted CW to upright CCW the right stick goes from 6 to 9 to 12 O'Clock because a left roll is required. You can practice making just these moves simultaneously on both gimbals while sitting in front of your TV and holding your TX. I find this helpful because after a few hundred transitions the movement becomes mechanical. It can then be fine tuned in the sim.
This type of transition analysis can be applied similarly to all circuits. One of my favorites is to begin by practicing full elevator circuits with just enough rudder and collective to keep the heli tumbling in the smallest circuit possible. First gain competence in the 8 basic orientations of this maneuver. Upright/inverted, forwards/backwards and CW/CCW. Now work on transitioning from upright CW forwards to inverted CW backwards. With time and practice you can do this move with one simple movement of the left stick from up/right straight through the center of the gimbal to back/left. Done properly the right stick need not move a bit from back/center. With a little collective management this becomes a tumbling circuit.
Try to figure out how this works for a rolling funnel.