Its a rough call as sometimes females have a plastral concavity that makes that method obsolete for determining male or female. Male tales are fatter than females as male reproductive organs are in the tails, whereas female reproductive organs are not. The wide anal plats is the best guess overall in my opinion as that is the "go-to" when plastral concavity does not work where I work for determining Gopherus polyphemus gender. The anal scutes on female tortoises must be wider than on males to allow their tales to expand to wide sizes while depositing eggs. Anal scutes that are not wide enough would likely result in damage to the females tail by being pressed between the anal scutes and egg shell, or the potential crushing of the eggs. If your sulcatas have wide anal scutes I would go for female. Note that they do get to be rather larger so over time it could become more obvious.