Perry reflex is achieved by adding reflex to a belly and backing at glue up, generally with all wood backed bows. You can add reflex to a sinewed backed bow but that is not Perry reflex as I know it. You'll also get better reflex using hide glue with the sinew instead of TB glue. TB glue and sinew makes a good backing but IMO you don't get the full potential of the sinew unless you use hide glue.
well said Pat, that's exactly what I think. And yes it is possible to back a bow with a premade (right word?) strip of sinew.
I have or better had two strips of them from a plains bow, which had thrown off the backing with a loud bang like a gunshot. Actually I used one of the strips to back a 5 curve plains bow. That strip was laying around my shop for years. I soaked it for two days, it became slabby and thick but staid together, it was easy to apply as a whole.