SuppressDuplicateDetection on update

We would like to have duplicate detection fire only on create. For this, we registered a plugin on all the required entities with the following code. 

if (ctx.Context.InputParameters.Contains("SuppressDuplicateDetection"))
{
ctx.Context.InputParameters["SuppressDuplicateDetection"] = true;
ctx.Context.InputParameters["CalculateMatchCodeSynchronously"] = true;
}

The code executes but does not stop the popup of duplicate detection from being displayed. Any help or thoughts on this issue? 

                if (ctx.Context.InputParameters.Contains("SuppressDuplicateDetection"))                {                    ctx.Context.InputParameters["SuppressDuplicateDetection"] = true;                    ctx.Context.InputParameters["CalculateMatchCodeSynchronously"] = true;                                    }