Reverse engineering a pattern in GH

How much of a ‘target’ is this target pattern? Are you trying to copy it as is? Doesn’t seem like that’s the case. Also, as you indicate, the reference pattern(s) vs the target one differ sufficiently.

Maybe to gain control start simple and search for/play with substrate?

Check out related topics - some simple others more advanced:

If you’re into plugins, you might want to look into loops: