Sometimes because of the design layout of the model, ideal tank positioning is hard to get. The model builder should definitely try to get it as close as he can. The point about firing up an upside down engine, is that it only takes a couple of drops of fuel puddled in the combustion chamber to drench a glow plug. If you are trying to start an engine with a high mounted tank, tilt the nose up slightly. Likewise, if you are trying to start a set up with poor fuel draw, tilt the nose down. I think it is a good idea to keep a set of hemostats around so you can pinch the feed line if you have a system that tends to flood itself automatically.