This is what we are referring to. They made the loop strap too long. You can’t take up any more slack on the car seat. On the Chevy I had the loop was at the back of the seat by the back glass and you could could get it tight.

Try going over the headrest. Or, is there anything that you could latch to behind the seat? I know we had to do that in Bradley's truck with the kids seats.

I tried it over the head rest and it made it even more unstable.

Unhook from the strap in the picture and run the clip through that loop and under the headrest. There should be another loop or anchor point behind the middle head rest. Hook to it and you will have plenty of room to tighten up the strap where it won’t move at all.

This picture is exactly what I’m dealing with rst87.

Well I found this on line. Seems like an odd way to have to install them but is the proper way according to some of the other videos.