What are you on about?Using the Acrylite acrylic calculator, properly top braced 2mm acrylic can't safely make a 30" x 6" tall tank. It requires .118" 4mm acrylic, with a top brace, much less a 19" tall tank. If you remove the top brace, like sticking a piece to the back, what good would 2mm be?
Not using the acrylic to build an aquarium,,, it's just to sandwich between the aquariums rear panel & the fudge unit to spread the load at the fuge mounting points. And it will also hide the fuge, or any ugly piece of glass siliconed across the back of the tank.