I'm not sure loops have anything to do with it for DCS. When you segment the power rail into blocks the topology doesn't matter so much. The idea is to limit any possible reflection or duplication of a single DCS packet on the power rail. There is no DCS recommendation to segment the common rails and my copy of the Companion states this as well.
In my case I only use the two fixed channels, one will feed the 1st level and the other feeds the second level. I have a pair terminal strips at the output of each channel so all feeder pairs are out and back to these strips. I have 5 pairs of feeders for the first level and each has two or three drops (one per block) connected to them. That's star wiring. (Second level coming this spring.)
I also tie all transformer commons together at the TIU channel outputs so both channels' common sides are connected electrically anyway. I thought I saw a 9 once, but when I looked back at my remote it displayed a 10. 
