6" of insulation is apx R 21, You dont say where you live or your Zone.
Im Zone 5 to -20f, code is R 35 but optimal is apx R 50-60+. So unless
you live in say florida or zone 9 more will help. What is attic sq ft.
your areas low temps and Zone. Ice dams, may be air leaking up from he
house, not enough venting, and lack of insulation.