Well, the Post Office considered their parking lots as part of the facility, which is different from the definition in 18 U.S. Code §930; so there is a precedence.
Per the Texas Alcoholic Beverage Code Sec. 11.49. PREMISES DEFINED; DESIGNATION OF LICENSED PREMISES. (a) In this code, "premises" means the grounds and all buildings, vehicles, and appurtenances pertaining to the grounds, including any adjacent premises if they are directly or indirectly under the control of the same person.
https://www.tabc.state.tx.us/laws/code/85th/AllTitles.pdf
Per the Texas Alcoholic Beverage Code Sec. 11.49. PREMISES DEFINED; DESIGNATION OF LICENSED PREMISES. (a) In this code, "premises" means the grounds and all buildings, vehicles, and appurtenances pertaining to the grounds, including any adjacent premises if they are directly or indirectly under the control of the same person.
https://www.tabc.state.tx.us/laws/code/85th/AllTitles.pdf