Glad that it is working for you :D:D:D
I slide one of those glass aquarium marbles (they have a flat side) underneath the backing once I have the sandwich all in place.
I can easily slide it to where I want to place the pin. It holds the fabric up just far enough to make pinning easy. I slide it from the top, just gently push it to where the next pin will be placed.
You can easily push the pin into the little gap the marble makes, and if you use the pin closers, just push the marble to the next spot and then use the closer.
This works well on tables too, it will help keep the pins from scratching the surface underneath :D:D:D