The best results I've had with cracks, is using an alpha. Not a cement/cracked concrete alpha though. I use a lightning alpha. Notice how the cracks are lightning-like in shape! Best of all, it's usually white on a black surface making it great for getting cracks without the noise of a concrete alpha.
I know this artist, and his robot picked my flower! Great support from other artisans on your concrete...lots of good ideas. I certainly know and respect the hours you put in to these creations.
I think you have the crack patterns pretty well down, but if you're going for something with more depth as in the thing on the right, wouldn't you want to move it down a bit at the major points of impact / collapse? That way you can have pieces jutting up or being sunken further down... it sounds like that is what you're…