I would usually fight for parties of 8 or larger just because I knew if they liked my service I would usually get a monster tip because they would tip on top of the 15-20% already expected of them.
that being said...I know some states have said (I don't know about Texas) that the "mandatory gratuity" is not legally binding...and if patrons really wanting to have push come to shove...they would win.
You CANNOT legally charge someone gratuity. Now...you could charge them a convenience fee...or call it something else...but you can't make them tip...and many states have said this...its just that most patrons won't fight the issue.