Prone Thoracic Band Pull - Lower Back?

I tried this today for the first time and it was extremely hard for me to get any mobility, but that was to be expected for what I am working on.  I feel the most effort was coming from my lower back as I tried to curl up my chest.  Is this to be expected or am I doing something wrong?

Zach

There is a lower back component, but in the context of the course it's not the emphasis. 

To help target the upper back, make sure that you are starting the movement from the head, to shoulder to chest, in other words working from the top down. The lower back shouldn't engage much until the end of the movement.

You can even work on isolating the movement by limiting the ROM and only working the upper back component until you've gotten a reasonable amount of movement there.