To be honest I am not sure how your current sequence value shows this is portable anyway. How is 130 a multiple of 50?

The spec is unfortunately very unclear on these points as it is on many points. It gets into what you think initialValue and incrementSize mean. And its easy to say that these are merely "schema export" hints, but keep in mind that these values existed way before JPA defined schema export. So I think that's not a valid PoV. And regardless, the spec is unclear as I said.