Set the horzontal horizontal... relative to the fuselage reference line.. with a flying tail, you iwll trimm it to the proper angle after you fly it a couple times.
A good starting angle would be to place a straight edge on the -bottom- of the wing, and set the horizontal parallel to that.
Possibly trim in a bit of up for the first toss.. be ready to push the nose down.. otherwise fly it and see where it wants the horizontal to be.