I tried out your code and see what you’re doing now. Your second background layer doesn’t fill the whole screen, so you can see around it, but not see through it. I assumed you would want a transparent bitmap, so for example, you’d see the circle but not the black border. (I changed the dimensions of your sketch to match my matrix, I’m sure it looks better on your matrix)
I’m glad this is working for you, but SmartMatrix Library wasn’t designed for this use case. You can’t position the extra bitmap layer anywhere but starting from coordinates (0,0) for example.
If you do want a full color layer with transparency, this is the only solution I know of compatible with SmartMatrix Library: