Some monti's sit for awhile before taking off. The SM and Sunset have been like that in the past for me, then go crazy. So long as you have good color and polyps displaying, give it a few more months.
My colonies will grow better under higher light and moderate flow, but ca/alk/mg levels also play a factor. Since I have been maintianing 450ca, 9-10dkh and 1450 Mg, they grow at a good clip. Some weeks I can see growth on the sunset on what seems to be a daily basis, other times it slows down, the spurts again.
I've also noticed that fragging helps growth too..