According to the Towers article, they had this to say about the height (or lack thereof):
"When the development appeared on the scene two years ago, some of our industry sources explained that Horizon is self-financing the project, and didn’t want to take on undue risk with a larger tower, since this building’s office levels and ground-floor bank space adequately meets their needs — and though we haven’t confirmed that with the bank, it’s the best explanation for 16 floors we’ve heard so far."
https://austin.towers.net/heres-our-...on-bank-tower/