TDY travel and BAS

Large portion of unit was recently on TDY travel to AK, and and had approved travel authorizations.

S-1 is coming back currently trying to deduct BAS for the entire month of January. There was only field duty (meaning CK/MRE) on this travel that was from 1/24-1/30. The rest was partial per diem (the 3.50 per day) because government meals were provided at no cost. Are they in the right here?