Insulating a fireplace insert?

I have a Lopi "revere" certified insert. I have seen at least one comment about insulating the hidden part of the stove to cut the loss into the chimney. I have a stainless chimney liner from the stove through the top of the chimney. Does anyone have any knowledge about the advisabilty of this action. I would probably use 1" insulation from the stove shop, backed up with standard fiberglass insulation to hold it in place.
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