I set up each channel as a single line, 1 channel. They are then modelled where the string lives on the display.
I then created a group containing the strings, and apply effects to that - such as a single strand effect, to get the chasing occurring.
It also gives me channel-level access to the individual strings, to control the colours etc as needed in the sequence.
That said, it's what works for me, others may have much more efficient ways of doing it.
I have my icicles configured as a custom prop with channels offset horizontally and vertically so that effects passing across the lights will turn on 1 section before the other.
It's also possible to fiddle with the string setup in xlights and make it a "superstring" which allows you to have different colours for each half.
Below is basically how I create the custom prop for my icicles.
1...3...5
.2...4...6