Actually Clarence Mather, the creator of A-6, wrote the following in a letter published in the 2002-2005 Winning Indoor designs in regards to tandems.
" Perhaps it would have been better not to limit the area of the stab. As Dave suggests, tandems might be fun to experiment with. The added weight of the large “second” wing might cancel out the added lift, because the rear wing cannot produce as much lift as the front."