Six inches for a leaf length is not that uncommon for dwarf sags. I just read somewhere that if you keep them densely planted, they will get longer/taller. If you want them to stay on the short side, spread them out a bit.
I have mine planted pretty closely because I like the look of several in a row. They are getting long for me too. Every once in a while, I pinch off the longest leaf right at the bottom where it joins the rosette structure. That doesn't seem to harm the plant at all. I have never tried trimming a leaf shorter. You could try it with just one leaf and see how it works. If you have CO2
you may see that cut leaf "stream" for awhile.
There is no harm in the leaves touching the substrate. My bettas like to hide (well, they think they are hiding!) under the bent part of the leaves. If you don't like that look, just trim off that leaf.
Don't worry about upsetting the babies on runners if you want to move and re-arrange the plants. You can leave the baby on the runner and move it too with no harm. I have found that the babies can be separated from the mother plant fairly quickly - either when the baby has two leaves, the leaves are about an inch tall, or after about 7-10 days.