I am installing SmartBaffles and additional insulation to my attic.  Since I have several bags of leftover ComfortBoard 80 (from an exterior project), may I use these in the attic?  Particularly around the perimeter?  I will fill in with ComfortBatt, as recommended.

Updated to add:  When my roof was replaced a few years ago, the roofer added much-needed overhangs.  In order to do this, he attached a rafter extension to each rafter, as required.  When I went up to install the baffles yesterday, they only go down to the rafter extension instead of all the way to the vent, leaving a foot to eighteen inches open to the attic.  May I just staple up cardboard along the perimeter in order to keep the air moving upward through the baffles?  In other words, the cardboard would go up 15-18 inches, the SmartBaffle would continue from there; insulation will be stacked in front of the cardboard over the attic floor.  Thanks to the pandemic, we have loads of cardboard boxes.

Or, would it be better to use the SmartBaffles in this way, stapling them to the outside of the rafters instead of nestling them inside each rafter bay?