Mine are getting on 20" tall now at their tallest with approx. 40 leaves on a 5" rhizome. So far the trick seems to be sunlight. The poor thing didn't do much of anything in a greenhouse, but started taking off when I put it outside and it got a full summer of direct NC sunlight. You might try doing the same with yours.
So far I haven't seen any daughter plants like Crypts put out. Instead it's growing much like an Anubias with many leaves on the main rhizome and small side shoot rhizomes coming off the main one. My guess is that cutting the rhizome is the best chances of vegitative propegation. I'd check with Tom, Bob, or Shaun W (I got my plant from him). They've got more experience with Lagenandra.