I have a 20 inch hearth extension in front of my came with the built-in masonry fireplace. The insert I've chosen is the VC Merrimack which extends about 7.5 inches into the extension. That puts me about 3.5 inches over the 16 inches I need for clearance. I'd like to add to my existing extension rather than tear out the old and replace. Is it reasonable to add another 4 inches of appropriate materials in front of my existing extension? I expect I can remove the carpeting, add the right amount of materials, and then cover it with either more white marble or some matching tile but not sure if that will suffice--please help. Thanks.