On your e-Visa is marked enddate of validity. If you enter Thailand before the enddate, you get stamped in depending your visa (tourist visa ex METV 60 days, non-O 90 days, non O-A 365 days, DTV 180 days).
I agree with you, as they want to see that you have money to live and leave Thailand without opening a growd funding group during 3 months.
But at the end of day, it's the immigration officer in front of you can decide to refuse entry (little battle between the foreign ministry and the internal ministry).