Your inspiration photo is similar to several terrific scapes that were in the top 200 IPALC this year. http://en.iaplc.com/results12/top200vote/
Use smaller plants behind and even tree shaped stem plants in front like #93.
If you want the scape to reflect the photo then the large rocks would be the mountains and you would have rolling hills of a larger scale ground cover in front and smaller to the rear. #134 might be the sort of thing you are looking.
I do like your current groupings though. What happens if you scoot the central group to the right a bit so it is better associated with the right hand group? The right hand group in front might be a bit larger than necessary too or perhaps the left hand group is a bit short. Depends on the height of the tank which way to go, right?