Seat limit of SYOS vs. Best Available online

I have a TNEW mystery that I cannot solve, so I turn to you fellow sleuths.

We've discovered that when online, a patron cannot select more than 10 seats if using Select Your Own Seat to choose seats. However, if Best Available is used, they can get more than 11.

What would be limiting SYOS quantity vs. Best Available? I've been in TNEW set-up and looked at documentation and can't find what I'm missing.