That seems… counter intuitive. I would say something has a high satiety index if something small can fill you up.

I think you may be confusing satiety with being "full".

You can eat 500 calories of butter and not feel even slightly full, but 500 calories of raw potato would have you full to bursting.

But satiety is defined as the state of being full. The satiety index should be based on volume not calories. Otherwise it’s not just unintuitive, it’s incorrect.

You don’t have to consume a certain number of calories to be full. You just need a large enough volume. Competitive eaters eat a huge amount of lettuce to feel “full” but it has almost no calories.

Satiety is defined as "the feeling or state of being sated"

Full != (Sated OR Satisfied)

Sate is defined as “satisfy to the full”