The insulation company is correct in their explanation. Basically their answers reflect the same concept of why "interior walls" are not insulated. Additional FYI it is a natural and scientific pact that warm air will always move to cold air. This is he phenomena of "passive heat." Like a sun room or porch with tile floors will collect heat during the day and that heat will be released in the evening to other parts of the house
Dennis (cut2it)
C&onstructi&on C&onsultant
Over 40 yrs. as General Contractor for new const. & remodel - retired with time for you.