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.
The way I understand gratuity in some of the places I have worked was because in large parties the turnover rate of customers is not as fast, meaning they are more likely to take up more floor space for a longer amount of time. Now they could end up drinking after their meal but usually they seem to want to stay around and just converse. This is fine and it’s why some restaurants charge gratuity for the time this is costing them while other patrons wait to be seated.
One place I worked only allowed me to collect on half of the 20% gratuity collected on tables over 8. Although anything the customer tipped over 20% was mine. Also some of this is allocated back to bartenders, prep and clean up. So not all of this goes to the waiter which many people that have not worked in the restaurant industry probably think.