Don't F.I.M. "miss" on the long side. I saw a grow the other day where 'a guy' had maybe 16, 9 week old plants in 2 gallon pots. The were at four days of bloom cycle and there was little height left. He showed me one plant that was 'his best' it had four tops. The others were still single apical meristem. He thought it was magic and not that it was the only plant that he topped (cropped, F.I.M.ed, whatever you want to call it) that he actually cut the stem and not just the leaf tips. This is a guy I can't tell anything to so I didn't try. I just told him that I thought his plants are too tall.
What I'm getting at is this, go ahead and try and fim. It's hard to get it where the stem will split at the cut into more than two stems. You can try it, but keep an eye on it to make sure you got the stem cut and not just a 'little trim' on the leaves. You can always cut it again a little closer, or cut it right below the leaves, fuck it, done.