A couple of the old designs had some really crazy amounts of downthrust specified. The gull winged one by Ontario Modelcraft is one but the name of the model elludes me at the moment. A flying buddy has built a few of them and they all needed a silly amount of downthrust.

Also the closer the engine to the balance point the bigger the angle has to be to achieve the desired effect. The ones that need this the most are also the ones with the power axis located well below the wing, which forms the lion's share of the overall drag of course.