RE: Where to install a fuel dot???
The idea of using the 3 line system is to make fueling a little easier. Ala not disconnecting the carb line in a coweled engine.
Your fill line needs to be long enough so that you aren't reaching around and turning your model over etc. but will not get caught in the prop or other flight/landing critical moving parts. Also as Kmot stated you want it to look somwhat decent.
On goof around planes mine come out the top and flap in the air. Otherwise they are neatly tucked up under the cowel but never long enough to reach the prop.
There is also a kit to mount a collar that holds the whole deal right to the side of the fuse or thru the cowel.