Tubs normally only have a water bowl and a hide.
6 qt - up to 200 grams
16 qt - 201-500
28 qt - 501-1200
41 qt - 1201+
But all snakes are different my lesser is only 200 grams and she was bumped up to a 16 qt at 150 due to her always exploring and her ability to keep eating.
But what you missing is tubs are more floor space vs height as well as water bowls are ALOT smaller because of no screen lids. The saying is the safer they feel the better. They like cramped areas and trust me they have room to eat and if not they will make room as they toss around trying to eat.
Also you should have gotten a 20 gallon LONG it looks that yours is the 20 gallon fish bowl one.