TPC 46.035 uses the following definition for Premises:
You can find that portion here: https://statutes.capitol.texas.gov/Docs ... /PE.46.htm"Premises" means a building or a portion of a building. The term does not include any public or private driveway, street, sidewalk or walkway, parking lot, parking garage, or other parking area.
Regarding if it's actually a 51% establishment or not, you can do an inquiry here at the TABC's website:
https://www.tabc.state.tx.us/PublicInquiry/Status.aspx
So, regarding your question, the 46.035 definition of Premise specifically excludes the parking lot. However, if the outdoor seating area is connected to the building, such as a covered or screened in porch, I personally wouldn't chance it.