Chimney Liner vs. Insulation Osburn 1800 Insert

[brink]

I finished installing my Osburn 1800 insert and am wondering if I should have installed a block off plate in the chimney. I have read that instead of using a block off plate it is ok to stuff insulation between the ss liner and clay liner in the chimney just above the insert. Is this an acceptable method to block off heat from escaping above the insert? If so, is unfaced fiberglass insulation ok to use? Or is the fireproof rockwool type a must use?
The insert is performing nicely, but I'd like to do the best I can to prevent heat loss. I have installed a 6 inch ss liner inside a 11x11 internal dimension clay masonry chimney. The top plate is siliconed to the clay liner and I stuffed a 6 inch batt of fiberglass insulation around the top of the ss liner just below the top plate.

 

[bluefrier]

Brink, you did a great job by adding a full liner with a top plate. Now, why not just add a block off plate to seal the deal? Personally, I would also go with rockwool or a similar high temp insulation for the liner but I think unfaced fiberglass should be ok.