I think Izy's idea of adding the quilt to the outside on the doorway alcove is right on target.
Attached you will find two views of the quilts I made for the west window in my sewing area. Cotton muslin as the backing, Warm and Natural cotton batting, and 100% cotton on the front. They cut down on the summer heat while letting in some daylight. Also, I have found them useful in the winter to provide a bit of relief from the harsh winter, even though the windows are triple glazed!
Notice daylight
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Window quilts to west window 2008 after remodeling
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