I don't know that you're doing any "wrong" per se - you can't necessarily force the growth to happen the way you want it, you can however usually tune the scrubber according to the conditions of the system.
I have found that text description of growth does not always match how I would describe your growth. So this is best to do with pics. The best way to take pics is by turning water off, lifting out the screen, and taking either a flash pic, or shining a flashlight on the screen so that it is under full white light. Take a couple from different angles and distances and pick the one that turns out the best.
Going back to where you started, is this still a temp setup or is your tank set up now?
#1: New tanks have generally lower biodiversity. As the system matures, the scrubber will also mature and you will tend to get more diverse growth. I'm starting to see this pattern more with brand new systems (even seeded with mature live rock).
#2: I had my fixtures bench tested on a high-end spectrometer and as it turns out, with the knob at the halfway point (6 o'clock), that is 25% intensity. That is still the recommended starting point, because this level matches the full-power output of most off-the-shelf growth lights. Turning the knob 1/4 turn upward (to 3/4 of max) gets you to 50% (doubling the intensity). Another 1/4 turn doubles it again to 100%. Starting at halfway and working up slowly to the 3/4 point is still the recommendation. BUT: if you are getting decent or at least consistent growth at any particular intensity, you can max out the photoperiod at that intensity and generally not have to worry about the scrubber growth reducing - because photosaturation has to do with intensity, not duration. If you happen to suck out the last bit of nutrients (or the last bit of a limiting nutrient) while running a long photoperiod, that's a different case (not photosaturation).
Before you do anything, give a quick synopsis of your system (age, bioload, feeding, etc)
