Have you tried the "where should I put my sub" trick with the SMS-1? If not, the position you have chosen might be the problem.

Put the sub where you sit and move the SMS-1's mic around the room to see where you get the best, i.e. most even response. Then put the sub there and tune the SMS-1 to the room.
_________________________
Robert S. Becker, Esq.
http://www.dcappeals.com
rbecker@dcappeals.com