I'm by no means a pro here, so it's just my opinion. Amano himself broke a lot of the "iwagumi rules" in some of his later tanks. In his "Complete Works" compendium book, he has some tanks with one big rock placed right smack in the middle, for example. He's also got some that point a group of rocks out in a sort of stellate pattern: ..\|/......\|/......
I marked up your photo to try to illustrate more what I was thinking. Red is one way to angle the rocks. Green is another way to angle the rocks. It's sort of like someone cut a valley through a fractured up mountain.
Just google "iwagumi rock placement" and you'll be able to find some images with the actual terms applied to the various stones in an arrangement according to Japanese gardening principles. It's cool, but maybe more in-depth than a lot of us want to get.
Bottom line is that if YOU like how it looks, then that's how it should be done.