Is the inability to chew using your back teeth with Invisalign attachments (to the backs of a patient's teeth) normal?

I am on my third set of tray and today I had to VERY large wedge-shaped attachments put on the back side of my upper two front teeth, to fix an overbite. Without the trays in my bottom two teeth hit these attachments almost immediately upon closing my mouth therefor preventing my back teeth from closing together. This prevents me from being able to grind or chew my food. I called and the dental assistant says this is normal and I will get used to it. It's not painful, just impossible to chew.