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I would try and get it up tight and flush wih the door threshold, but I would also use molding on the edge. But not 1/4 round, instead I would use a nice solid wood flat mold to create an extension of the threshold, even if it is lower. Like a 1/4 x 1 inch oak strip mold. Taper or round off the ends nice at your base mold on the sides of the door.