The article mentions sticking close to the thrustline indicated on the plans. The plans indicate right thrust but no down thrust on the engine. Uravitch is a pretty well regarded designer. I've built one of his delta wings and it was a great flier. As such I would stick with things as indicated on the plans. Most of the stuff that I see about incidence angles pertains to the BUSA airplanes, in particular the Fokkers. As a rule WWI planes make a lot of lift and want to zoom climb at full throttle. I've had several WWI planes and they were all happiest at 1/2 to 2/3 throttle. I would expect the Se5a to be much the same.