The only discus models from your description that I can find show a fixed stabilizer with movable elevator.  And it doesn't appear to have flaps.  First off ensure that the elevator is sitting at zero to the stabilizer.  Otherwise you'll get a false reading. 

The other issue is that on a high speed sort of model where you're expected to move the CG more towards the rearward limit you do not require a lot of Longitudinal Dihedral (LD).  So the designers may have expected you to just use a few clicks or turns of up trim on the Tx or a clevis in the pushrod system for the elevator.  If this bothers you then add a wedge shaped shim to the stabilizer that provides a one degree negative angle to the fixed stabilizer and adjust the elevator pushrod to do the same to the movable elevator so it is all smoothly faired. 

From there go and fly and test the CG location until it's as far back as you can comfortably tolerate and then look at the elevator trim position and adjust the wedge shimming as required.