"the stems are shorter when it doesn't have to reach out to get light. Clearly, in my indoor tower - it doesn't"
Unless you are a commercial indoor grower using a high-end ($$$) professional grade lighting system, There is no such thing as "enough light" when it comes to growing indoors.
You may find this article helpful:
The Secrets to Successfully Growing Cilantro (and Coriander)
BTW... I suggest that pop the top edge of those grow port plugs out of the growing ports so they press against the white edge of the tower section above. This will mitigate the possibility of nutrient solution leakage from the occasional stray drip coming from the internal drain holes (it also makes it easier to remove the plug).
Thanks. Already read that great article. Really love the blog posts. Always good stuff.
It's growing pretty well so far. I had never grown it before so I was wondering if the low growth was normal or the result of something I've done.