Elendir, no, the Heliodorus reference is in a work of fiction and so represents not actual tactical doctrine but perceived reports ofPersian cataphracts in the Late Roman period. It exists alongside Roman historical writers as an example of the popular imagination. Having said that, the details are interesting!
Fiction? Yes, three plays finished and out at theatres for review (some positive feedback but no productions yet!) - 1 is Late Roman about Hypatia. I am slowly chipping away at a novel which culminates in the battle of Hadrianople and its aftermath. Hence some of the research above!
Gaiten, thanks for the advice and insight. Again, it only exists as a work of Roman fiction and so must be taken with a pinch of proverbial salt! It represents I think how literate Romans thought about the cataphracts more than describing their actual battlefield use!