As the title says, I'm wondering about top plate liner compatibility. I have an M-Flex 8" liner I need a top plate for. I need a 18x18 terra-cotta top plate. I called Rockford as they sell the M-Flex and components for it but they didn't have what I need in stock nor did they have a price. So I'm waiting for them to get in touch with National Chimney for said info. Thing is I need to get this done so I'd like to keep looking in case this falls through/takes to long. So, are these things interchangeable or do I need to stay brand specific? Also, any suggestions where I might look for such a top plate would be much appreciated. Thanks