Mistral DB killer FAIL

looking for others experience on this. Ordered the Mistral DB killer specific for my Mistral Carbon. Mounted it using a few thin washers between the DBK and the exhaust wall, so that the DBK would be centered, as it is slightly smaller diameter than the exhaust. Photo shows what happened.

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I know I initially had it very tight, to German torque specs, but it failed. Now, I could just grab larger diameter washers and try again, but I'd like council.

I show it clamped by vice grips to show the diameter difference. It was suggested that maybe it's too small and should be a slip fit. For those running a Mistral with DBK installed, is what you see in my photo consistent with your own? (Looking at you, Pete.)

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Thanks in advance for the assist!