Kraft-faced insulation in an attic floor allows a constellation of mouse houses.
They love the alleys from on-flat header framing. Tighter quarters in lofts atop framing are not kept clean.
The best response to mice in-attic is habitat destruction, by removing the facing. Tightly fill all crevices with insulation fragments or batt trims. The facing here always did more harm than good. Smooth facing has less wind resistance, than tufty unfaced batts.
I advocate elimination of all kraft facing in new batt manufacture. Instead apply a vapor permeable air barrier facing like house wrap, as an attachment means and as a stiller of air circulation within batts. Have as many faces as you wish in any stack. Place the face in any direction, downward in a crawl space or basement ceiling, outward on a knee wall, where the barrier serves to contain dust from human contact. I offered this idea to my favorite manufacturer, Johns Manville, in August, 2011. No response yet from JM, so let any manufacturer try it.
Wrap-faced batts should not be at the base in an attic floor.