Miles,
Those are very interesting Peruvian rays. I do not believe that they are castexi morphs (DW...notice the word usage). The pattern is similar but, I do not believe that the body structure is. In my limited experience, castexi are a bulkier ray that get very large in size. The rays you have look to be more dorsally compressed and have a thinner body especially as you move toward the outside of the disc.
Just my two cents.
Colin