Height is good for severums but footprint is the main thing, territory and swimming area, both important, are primarily about footprint, meaning length and width. Height won't make up for not enough real estate with the fish you're talking about. Tank size is a contentious subject, a lot of people have rigid opinions when in truth there is some flexibility. Still, while I don't know what size you have in mind, there aren't many scenarios where you'd want less than 4 ft. length for a severum with geos.